Notion has an nTempo track that allows real time control and recording of tempo. You tap the tempo and the playback follows, optionally recording the new tempo map. This would be great for adding subtle tempo changes and even formats. Love to see something similar in Sonar.

Me too. This has been requested previously in various iterations. (I initiated a post requesting a realtime tempo (not tap as you suggest, but using a midi pedal.)) Many have asked for the tempo view to be reworked into a tempo envelope, which if it were midi assignable would serve the need. I like the "conductor track" idea too which I think Cubase uses.
I didn't vote because I've already voted previously. But a big +1 here.

Was open the phone a few hours ago talking about this very subject asking them where the tempo data was at yes they show open up more events would only help workflow.

+1 for recording tempo changes with a midi controller.