EmuMovies has an extremely dedicated community which backfills all artwork, including backgrounds, boxart front/back, 3d box art, title screen, screenshots, map screen, cart images, banners, low and high quality gameplay videos, advertisements, etc.
I'm currently using said artwork with Rom Collection Browser in XBMC and Hyperspin, both which have some pretty serious flaws.
Native support wouldn't be necessary, as EmuMovies provides a client to download artwork for your rom collection, but it couldn't hurt.
The bigger ask would be to allow defining a directory structure for each type of artwork on local storage, so that it wouldn't be necessary to fetch from scrapers unless it wasn't available.
EmuMovies stores data in the following format:
HQ Movies: %PATH%/%SYSTEM%/Video_MP4_HI_QUAL/%GAME%.mp4
Movies: %PATH%/%SYSTEM%/Video_MP4_HI_QUAL/%GAME%.mp4
Background: %PATH%/%SYSTEM%/Background/%GAME%.jpg
Box Back: %PATH%/%SYSTEM%/BoxBack/%GAME%.jpg
Box Front: %PATH%/%SYSTEM%/Box/%GAME%.png
Box 3D: %PATH%/%SYSTEM%/Box_3D/%GAME%.png
Title: %PATH%/%SYSTEM%/Title/%GAME%.png
Screenshot: %PATH%/%SYSTEM%/Snap/%GAME%.png
Map: %PATH%/%SYSTEM%/Map/%GAME%.pdf
Cart: %PATH%/%SYSTEM%/Cart/%GAME%.jpg
Banner: %PATH%/%SYSTEM%/Banner/%GAME%.jpg
Advertisement: %PATH%/%SYSTEM%/Advert/%GAME%.jpg
Hope that helps!