It might be helpful to put together a list of functions that the
toolserver supports but that labs currently does not; such a list could
serve as a basis for talks with the WMF.  Perhaps the labs folks could
makes some guesses at when those functions would be available and stable
there, which would give everyone a better idea about how long the
transition would realistically take.

If I am not mistaken, one of the big items is the ability to run
expensive db queries without impacting production.  I don't believe this
is possible from labs right now, and I'm not sure what their plans are
for that.

Ariel

p.s. this post is by me as a former toolserver user, having nothing to
do with my status as a wmf staff member etc.