SmartGit 22.1 will show the merge base in the Commit view.

This option will be present in upcoming version 22.1 Preview.

We do not have any release date planned. But the first Preview might not be too far away. You may follow the Blog's RSS feed or @smartgithg on Twitter to get informed as soon as it is available. 

Version 22.1 will support diff.<type>.textconv.

For 22.1, the Changes View will support diff.<type>.textconv.

One problem I see here will be the disruption when switching e.g. from the compact Diff to the (necessarily) full Blame.

In the Preferences, Low-Level Properties you can disable rebase.disableRebaseMerges.

This behavior is expected.

Are you referring to the Log Graph's Follow Only First Parent option? If so, I can't reproduce this problem. Please send some small test repository for which the problem is reproducible to smartgit@syntevo.com.