There is
community work underway
to update GWT-RPC itself to use jakarta.servlet packages, and the same
idea could be applied to gwtplatform. Unfortunately, the
gwtplatform.com
domain is still owned, so any fork could not take over the groupid, but
would need to pick a new one, which might cause some irritation when
upgrading. I do see that the domain is scheduled to expire next year,
but that probably isn't long enough to wait. It might be possible to
contact the former owners to get permission for this work to be
published as well. If you take that route, I'd be interested in being
involved.
I've used the eclipse transformer before, and personally found it to be more trouble that it is worth.