Aye it is a reasonable fear.
Baring immediate notice by WOTC of a true project in the works that doesn't specfically say they will support at least the 3.5 I think your ok until at least January '08.
While I'm sitting on the sidelines waiting, I think our best bet would be throwing our support to one of the ones left. PCGen or RPG Xplorer, I'm sure there are a few others out there that might have what we want. But without the 'official' data from WOTC its just twisting in the wind doing self-support.
Now if a WOTC person is reading this and has any influence on said 'theoritical' project, perhaps saying to that project team to build for 3.5, then provide add-ons later for supporting previous additions. A 3.0 support wouldn't be that hard as it would be a few minor tweaks of the core rule books and the addition of the other splat books. A simple book inclusion like one that SpellGen uses in which books to pull spells from.
If as a side project they were to add any 1E/2E support, I would venture to guess their sales of the product would jump higher than suspected. Yeah it's a pipe dream, but there are many out there who are still loving it 1E style and never even attempted the jump into 2E let alone the 3/3.5E world.
But realistically I think they would have a heck of a backlash if they were to withhold a project such as this for 4E immediately after pulling the rug from the only 'official' supporter. As it is I don't think it would be to very hard to search for some LST files for PCGen of other's work, and for whatever custom files that RPG Xplorer uses.
Yeti