Tuesday's PSP firmware update appears to have paved the way for downloadable NeoGeo and PCEngine/TurboGrafx-16 games.
Folders for both formats were added to the XMB menu, according to Tom's Guide. There they'll sit with folders for established content such as Minis and PSN games.
NeoGeo and PCEngine/TurboGrafx-16 games are already offered to PSP owners in Japan, and their journey West was spotted on US ratings website the ESRB recently.