What I liked about Trent's original bug report is that it didn't just bring up a generic issue (cannot build with read-only source code), but clarified that his concern really was graminit.

So I'd like to declare that this (graminit) is the focus of this issue: any other aspects of read-only source trees are out of scope, and should be reported separately.

That said:

As for typeslots.inc: this shouldn't really be an issue for a released version of Python, since its tarball should include the generated file, and the timestamps should be in an order so that generation is unnecessary. This should be the case for all generated files that are also checked into Mercurial. For checkouts from Mercurial, you should do "make touch" after an update, as this will bring the timestamps in the right order.

It seems that graminit is missing from .hgtouch (in which case Trent's patch probably wouldn't have been necessary, except that it also fixes older branches). But that is again a different issue.

As for sysconfigdata: this really should be a separate issue. It's more difficult, since installation and packaging needs to pick up the file even if it's not in the source tree.