I find your idea interesting; really for the part of having some showroom or a library of games made with UE4 with more highlight (with search hability, categories, platform, etc… more like a store). Actually, from the front page of unrealengine.com there is nothing like that (to promote the games&the engine). some time a blog news on a specific game, or else you really need to look for it to find the wiki page A new, community-hosted Unreal Engine Wiki - Announcements and Releases - Unreal Engine Forums where there are games made with UE4
its just wiki pages, that mean the data are already there most of the time with link to the steam page, official page, etc, just miss some UX element.
If epic want to turn it into a full store, why not… but I’m less confident in the fact that it’s a good opportunity “for sure” - for indies and for epic; because players already have big platform where they can found games and have discussion, etc.
for now the community of unrealengine.com for me is really centered about the creation of game (dev, creator of content&games and modding); so not really the full target market for having success selling games. I mean the marketplace make sense in terms of the target market audience already here. Your indiemarket, really less; I think it would required quite a marketing effort from epic to attract customers to turn such thing into commercial success (perhaps I’m wrong, I’m not an expert of marketing; but I guess that’s why for now list of games is just a wiki thing 
).