It has nothing to do with the reboot. GR made a choice only to do 4 books and could have done a deal to do more and the people involved are industry people who largely got the job because of their prior work (like Steve and Chris who actually worked on a prior DC rpg) and could have done a deal for more books. So hoping for more is like hoping for the second coming. Be thankful for the first coming and treat it like it is the good news. You don't really need more than those 4 books. You have a core rule book, 2 character books, a universe book. Want more: look up DC.wikia. Want maps? Goggle it. You don't absolutely need any of that.
If that was in the cards it would have been done in the initial plan. More than likely, GR would not want to anything about the reboot since that event, like most comic defining events is merely a temporary thing so any changes to the characters might simply be that. I don't know if you know this but both Captain America and Thor died recently (like 2 years ago). That's not long ago yet they are back and yes we now have essentially The Hero formerly known as Captain America and a Captain America now in the Heroic Age, and yes they seem to have this set up where they are franchising the Avengers but you could still make an iconic version of those Marvel characters and ignore all of that.
Whereas, the MWP approach to the new Marvel rpg will not be like that they specifically will have summer event sourcebooks and I think will do prior ones too like Civil War or the skrull invasion and they'll have a specific sourcebook.
Now would GR do a Blackest Night/Brightess Day or an Infinite Crisis sourcebook? They could and it would only be about that series of events and any changes to a character so that they might not need to put a whole write up for a character but rather tailored info.
But in a way that is running specifics about a campaign world and who knows how many people might want that. One assumes many but anyone is free to find an another already printed DC sourcebook to such events and using their nifty MnM core book and imagination they could easily do that. Sure it is nice for someone like Steve or Chris to compile information for you in a nice compact digestible form but apparently there are at least a good eight dozen capable writers on planet Earth who can do that same thing. You included more than likely.
If you want to play Blackest Night go for it you have stats for the Black Lanterns, make changes as you see fit.
Other than that, the sourcebook that might be viable is a targeted one like JSA where you really focus on just the JSA and fill it with history of them in detail and stat out minor charcters and odd villains that might have only seen one story line, plus maps of their HQ and all that. I love those sourcebooks but most of that info is commonly accessible and probably has been done in prior DC rpg's like the one that Steve and Chris worked on. Plus it gives new desire to finding and purchasing old books which is a boone to people who make business's like Noble Knight Games who want you to go and buy an old JSA sourcebook for 17 dollars form them and being good business people they might increase the price to 32 dollars knowing there is a higher demand. As good libertarian capitalist you would say 'good for them' and gladly fork over that extra money to support their effort.
I don't mind if more DCA books are made. Sure it would be great if it did but then after reading the new Cortex (found a pdf of it free) I think I like the system and will buy (invest) in the 16 sourcebooks if I like the first couple of books but I will continue to play and love MnM and know there will never be a Marvel Universe Adventures. Sucks for sure as it would have been great to have two four book sets (DCA/MUA) but oh well, I guess the gods did not fate it to be that way.
I found a way I think to convert from Cortex if I wish. That system is actually nice and has some similarities, like Plot points and a target number system that is similar. They both use target numbers and MnM has DC 40 set to impossible, Cortex 38 as a critical success impossible task. I suppose I could play the Cortex system and just increase the target needed by 2 so that they are both 40 = critical impossible success and yet Cortex seems to go by a 4 increment increase and MnM by a 5 increment increase (ie 12, 16, 20, 24, etc.) and (5, 10, 15, 20, 25, etc.) so they are mechanically similar. Though I think I like the idea if instead of two dice d12 + d6 to get the number I would want that added to a base number and that is one reason I like MnM's core mechanics. I read the intro for Cortex and basically the designer liked the experience of rolling multiple dice and why the core mechanic is designed to use them and you increase dice so you go up steps d2, d4, d6, d8, d12 and then instead of moving to d16 or d20 or d24 (yes there does exist dice for those) you double up so d12 + d2, d12 + d4, etc. so by step 12 you get d12 + d12. Since you have a target number of 31 lets say and you roll that I assume the Marvel game will have a guy like the hulk have 3d12 (d12 + d12 + d12) so that he can achieve a 36 but since hulk can actually achieve critically impossible strength feats for that he probably has even higher like 3d12 + d2 or something like that is my guess but I think if I used that system simply having a base bonus.
But beside the mechanic they will do a lot of sourcebooks unlike DCA and its been a while and right now the only marvel stuff I own is the old TSR stuff. I did own marvel saga and the MURPG and they had some of the avengers/x-men mansion and stuff (Reed Richard's guide is among the best for Marvel SAGA for this sort of thing) but I also still have the old DC rpg from Mayfair games Batman sourcebook.
Since GR won't produce something like a Batman or Superman or Lantern Corps sourcebooks anyone know of links to other ones, even if they aren't rpg related that has pics of all Batman's gadgets. I know there was a prior Batman rpg too. I personally would love a Gotham City boxset with the big fold out Gotham map on one side and the bat mansion and cave on the other in full color. The one I have from the old DC rpg (mayfair) has a map like that but its not gotham and it is in blue and white only.
Instead of a call for GR to produce such things it might be more fruitful to compile a list of links on the forum to products that can fulfill the need we are looking for (like maps of DC locations). Perhaps one of those people of the eight dozen good writers of the rpg industry can compile a list since when they work they go about finding such information sources in the first place to rewrite and compile it in a new sourcebook. I know they don't just go to DC.wikia to learn about batman they find other sources. What are those sources?