Hi JS + all,
we are using Tuscany C++ in one of our projects, hence we/I have some
personal interest and also would like to contribute, if possible.
Tbh, I don't know details about C++11 (will read a bit) nor the other
things you mention.
Great! Papers from the C++11 standard work groups are available on open-std.org
there . The final ISO standard is not free but the last draft  is free. If you just want a high level overview there's one on Wikipedia . Hope that helps.
One thing though which appears quite important to me is that the various
patches we/I have done (most/all (?) submitted to Jira) and other people
are incorporated into the general code so that they are in the next
release if there will ever be one ... and of course this is easier
before any refactorings.
I found one JIRA with a patch from you , which looks like a change to the SDO + Axiom support in the SCA-Native-M3 release.
The C++ trunk has already gone through some refactoring and quite a few changes over time since M3... There's no SDO anymore (like the Java trunk, which I believe dropped SDO as well), the composite files use the new SCDL from OASIS, the runtime integrates with Apache HTTPD, etc. There's still an integration with Axis2C but I've not looked at it for a very long time.
So, if you're still using SDO you'll probably want to stick to the M3 level, but I can help apply your patch to a maintenance branch off M3 at some point if that helps.
The other thing: Are the planned changes going to modify the API
interface or is it just internally?
The C++11 changes only apply to the runtime internals, but again if you're using the SDO-based API from M3, that already changed a long time ago.