Hey Matt!
This is one feature that I dearly wish to see in Vital.
First of all, this synth is honestly amazing. It has truly blown my mind out. It is, in fact, a masterpiece, specially for those who cannot afford costly plugins out there.
Back to the topic, this feature can really help people like me who use it more to learn synthesis and play live than use it in a DAW. I’ve seen other instruments that allow setting internal tempo. Now since we can already modulate the tempo using the matrix, I see this ability as being hidden somewhere. It turns out to be inconvenient to set up a macro to control it.
I see this as an additional box sitting in the Advanced menu. Or maybe on the titlebar? (It works like LFO frequency knob (box? 
), which is dragged to change the tempo)
— The LFO frequency control
It can be automatically greyed out when running in a host, with the ability to unlock it and use the internal tempo (even in a host).
It should not be much of an effort to unhide it since we can already modulate the tempo through the matrix.
I have an idea for the position. What about a right-click menu on the oscilloscope with a ‘Tempo’ option. On clicking the option, the Oscilloscope-cum-Spectrum Analyser doubles (triples?) up as a Tempo setting, with the choice to bypass the host tempo when run in a DAW.
Maybe something like this:-
