I wouldnt be at all suprised if the next Ableton Live we see is still 32 bit.
However I can imagine it shipping with a 64 bit bridge, quite possibly licensing jbridge or similar to deal with 64 bit samplers etc and at least allow moving heavy plugins into another process. Mor likely a small subset of Live wll get ported to 64 bit to provide a 64 bit process for heavy plugins.
The reason for this is I suspect that for a full migration to 64 bit a number of things probably have to happen:
1. Any licensed technologies need to be available in 64 bit (Elastique for example, which I bveleive is available as 64 bit, and of course the licensed, adapated/rebadged plugins).
2. Core engine and plugin suupport needs to work as 64 bit.
3. For now, some kind of bridge back to 32 bit plugins is still needed (or they coulod take the view they if you want to run 32 bit plugins, run 32 bit live - harsh, but possible).
4. Max For Live - I dont know how this integrated. Max/Msp AFAIK isnt 64 bit, 64 bit doesnt even seem to be on the horizon yet. In edit mode, I guess there is some kind of interprocess comms going on, so potentially it can be bridged for editing at least. As you can run stuff in the editor, then I have to assume they can bridge from a 64 bit Live to a 32 bit Max/Msp relaively easily. If not - Ugh - thats a big job.
5. If/When MAX goes 64 bit a load of really useful 3rd party externals simply wont work. For me personally some of those externals are the entire reason that I use M4L att all, so it immediately becomes totally useless until those externals are updated (assuming they ever will be). If MAX was allready available in 64 bit, I would feel alot more comfortable about this.
Now if Ableton are doing the job properly, they need to have been on it for quite some time, and will probaly need alot more time to finish the job - quite simply they have more problems to sort out than any other DAW had when they made their transitions to 64 bit (old legacy code, both OS platforms, VST and AU plugin platforms, a core engine that is simply horribly old now, then add M4L and serato bridge etc).
Im guess serato bridge is a fairly minor problem next to the rest of this lot.
So, I suspect we might see a 64 bit VST and AU bridge rather than a 64 bit application next time around - because this means its easier to keep some users happy with much screamed for core engine improvements that are long overdue and by far most importantly, keep the ableton marketting and product managers happy with new marketable features, while the techies get more time to figure WTF to do with the MAX engine...
Nothing to see here - move along!