Perhaps something like having forums set up similar to: (looking to the future

)
Version 4.0 (separate forum)
Version 3.5 (separate forum)
Versions 3.0 and older (EOL) (separate forum with a set of sub-forum groupings:
Version 3.0's
Version 2.0s and older )
As versions hit their EOL, their topics could be moved into the appropriate forum section. (And/or whole sections moved from the main support section to this other section for older versions...)
It would just mean a bit of housekeeping & moving the furniture around here every once in a while....