With a recent patch, Tycho has achieved a major milestone that allows it to be a viable replacement to build SimRel repo in place of the very specific CBI aggregator. Specifically, Tycho now can validate a build plan without downloading all artifacts, so it can allow the Gerrit patch/CI feedback short feedback loop.
The principle and benefits of this change consists in getting rid of CBI aggregator specific files, models, builders... which no-one beyond a few privileged (?) ones know how to deal with. By moving it to more mainstream and better known Maven+Tycho+category.xml stack, we allow more people to participate in the maintenance of the SimRel aggregation; and we also get rid of one brick to maintain (CBI aggregator) in favor of a well maintained and active one (Tycho). This will overall result in some resources saving and SimRel entry-barrier being much lowered.
Of course, there are some features of CBI aggregator that don't have equivalent in Tycho, and the other way round; sending emails for example wouldn't be available anymore. But times have changed since the introduction of CBI aggregator (called b3 back then): CI rose, Code Review rose, all this DevOps things basically matured and has brought solutions for the use-case that were directly supported by b3. Not so objectively, I don't know of any feature of CBI aggregator for SimRel build that we would really miss when moving to Tycho. I don't the replacement this will either increase difficulty of contributing to SimRel or to maintain it.
I think all that stack is mature enough, and the value/savings in changing to Tycho is compelling enough to consider this migration for 2021-03.