I haven't heard any further feedback on this settings storage. I am still favouring the new in-WC config file ('wc/.svn/config'). It seems straightforward and understandable with hopefully not so much potential for bikeshedding (no need for new command line options or commands, for example).
On the 'multi-wc-format' branch I have completed the required test framework modifications to allow testing multiple requested versions (test suite '--wc-format-version' option; see the thread "Multi-WC-format branch: preparing for merge to trunk"). Next I am running tests of pristines-on-demand merged with multi-wc-format. As expected, tests fail when requesting the older format, because right now it unconditionally expects the new format. The pristines-on-demand behaviour needs to be made conditional on WC format. At libsvn_client layer that's simple, while at libsvn_wc layer it is also simple but requires a little bit of futzing to make two variants of some existing wc-db queries, one with and one without the extra 'hydrated' column. Once that is done, I plan to return to this per-WC config option storage. - Julian