Hi Guti,
Thanks for your interest.
Currently Gary and I are working in 'stealth mode' on the next version of MultiBit (MultiBit HD) so it is mainly maintenance work being done on the MultiBit code.
If you'd like to write code for a bitcoin client I would recommend creating your own !
Mike Hearn wrote a post in 'Alternative Clients' about how easy it is now to write a client:
https://bitcointalk.org/index.php?topic=323541.0The reason I suggest that is that MultiBit has now become a bit of a victim of its own success. There are so many users now that I have to be ultraconservative with making changes. Everything has to be as robust as possible, fully unit tested, everything documented on the help pages and regression tested on each release. As much as possible it has to be both backward and forward compatible with earlier versions of MultiBit and those not yet even written.
(It's actually getting a bit painful).
Mike's example wallet app is a lot cleaner code than MultiBit and would be a nicer codebase to start with.
Having more SPV clients would be better for Bitcoin in the long run too as we should have more decentralisation.
Something to think about anyhow !
:-)