"a tempo"

It is in the works, chances are that it'd be part or 4.2

"Please make a option to insert "a tempo" if this feature does not exist."

Honestly, I don't think that this is easy to automate. Think about it.
- What is the difference between Tempo primo and A tempo ?
- When you say A tempo, do you mean the tempo before that recent allargando, or the tempo before the rit. which was marked 20 measures earlier?

I handle this by creating a little text file with a Tempo Map, like this:
m.1 Adagio 71bpm
m.11 accel. 75, 78. 80 bpm (separate tempo marks)
m.26 allarg. 78, 76 bpm
m.23 rit. 74, 72, 70 bpm
m.26 A tempo 71 bpm
... and so on.

If you want a sensitive playback, you have to get involved. Don't just rely on automation: be prepared to put in the exact bpm manually.