Spong.com (always a good source of wacky rumors) is posting that an unnamed, off the record source is saying that we are going to be looking at a MAME-like feature on XBLA that will include tonnes and tonnes of different games (obviously not all of them as some of the publishers no longer exist, and some of the names start with Nintendo).
The Article also talks about an unspecified “major contribution” from Sega to XBLA to be announced at E3 next month.
As for validity of the rumors, we you can expect that a bunch of classic arcade games will be announced, but I really can’t see them suddenly jumping the number of titles to come even close to a quarter of the 3296 games. Also, everyone should be expecting Sega to announce support for XBLA (again) at E3.
You can read the article here