Could you clarify what do you mean here?
As far as I see there is a redmine issue importer so we can use it as base to import all issues from roundup.
I think we can simplify the styling bot by just running flake8 on CI. This will give the user the full lines details on the build output. One drawback is that there won’t be inline comments, but as far as the lines are shown on the CI output there is not issue for me.
Indeed we can avoid running the tests if the flake8 does not pass which will force the user to fix them before getting a review (and also the same for failing tests).
This may depend if we prefer to keep it running on our servers or use the hosted services. This should be discussed also if we prefer going this way.
IIRC we started using drone when it was not stable and this caused us to migrate to new APIs because of incompatible changes (event we lost the build history). So as far as the workflow is suitable for us I think we can consider doing the same for Mercurial+Gitlab which probably is more stable.
As far as Python2 is no longer maintained (for 1 year already) I do not see what could change in 2 years to make things more complicated. Indeed I see no plan from google app engine to deprecate python 2.7.