Multiple recording channels is a possibility. The one major problem to consider is that it can't be backward compatible - the current recording handle (RECORDCHAN) would have to go, and the recording functions would instead require an extra parameter for the handle - and so all users' existing recording code would need updating.
So, it's probably unlikely to be in 1.8 (coming soon), but maybe a poll for whether to do it for 1.9

Regarding multi-instance usage... note that there's no need to have multiple BASS.DLLs in your distribution - you can simply create/load temporary copies when needed, as in the MULTI example.