Before going forward do some planing and be clear WHERE you/we are going. To do that put together a grop of:
-site owners/builders - people that create/need diferent tipe of sites/solutions (company site, personal site, blog, online shop, catalog-compare/matrix, forum ...);
-module developers - people, who create diferent type of modules;
-designers - people that develop themes;
-webmasters - people who manage web sites every day;
-some end users
and ask them what they need from XOOPS in their work, what they would like to see in xoops.
Be absolutely clear what the future XOOPS will be (one developer playground, the next Joomla /do we need another one?/, easy to set up and use system for end user personal sites, stable and secure business level system ... something else. AND IT CAN'T BE ALL OF THAT IN THE SAME TIME!).
Evaluate the current situation of the XOOPS code and the options. Code up to 2.0.13.2 is one style, 2.0.14, 15, 16 is messed with another style and 2.2.x is very diferent.
-Building on 2.0.16 foundation will make the code harder to read. And personaly I don't agree it is clean code in 2.0.16. Example - for theme designers one code for top blocks and another for bottom. Lot of old code is still left and buried deeper in files - xoops13_header ... Do someone using XOOPS 1.3 themes and do they work?
-Bringing 2.0 and 2.2 together will create heavy code too.
Agree on where XOOPS should go and what it should look like - architecture, features ...
Separate the management an development teams - developers should write the code, managers should help
them stay on the agreed path and coordinate with other tasks - betatesting, themes, and so on ...
Make the team with people, that accept the path and only then start development
Sorry if my english is not very clear ...