I was looking through the hd100 brochure and it said "future support for 1080i". what's that all about? is there an upgrade forthcoming?

I think with the 110 release the last upgrade the 100 will see is the A upgrade.

You are referring to a ProHD Brochure, not just a HD100 brochure. ProHD encompases the HD100, HD110, HD200, HD250, the BR-HD50, and their PAL counterparts, although in the booklet currently only the HD100 and the BR-50 are included since the others are new. In the booklet JVC stated that a future ProHD XE will come out that also allows for Uncompressed PCM Audio.

My feeling on this is that JVC will skip right over 1080i and in the future, maybe at NAB next year, and release a 1080p Model. I really see not reason for them to go interlaced at this late in the game.