Rubbish. The main Ukranian MBT in service is the T-64 and T-64B. Only recently did they manage to get a single tank btln modernized to the T-64BM standard. No line units are equipped with the T-84 (or even the T-80) to the best of my knowledge.
Diplomatic pressure, cutting of relations, yes. Absolutely. Military action? Unlikely.
I'm afraid people here don't realize just how bad the situation is in Ukraine. The Ukranian economy has never recovered since the collapse of the USSR. Their armed forces are ~300 000 strong, but their military budget is tiny. New equipment, when purchased, is purchased in token amounts. Their military structure currently is a half-way mix if small brigades (2-3 thousand) and large brigade (i.e. a soviet division renamed into a brigade).
The equipment consists primarily of BTR-80, and BMP-2, with money for maintenance and training being scarce. None of the new BTR-94, BTR-3, etc. have been purchased in appreciable quantities. The SAM network consists primarily of unmodernized late 80's soviet SAMs in various states of disrepair. Interestingly enough even the Buk M1 SAMs they sold to Georgia were taken off of active duty in Ukraine.
I don't know what kind of flight hours the Ukranian AF gets, but I suspect the average numbers will be horrifying. Work in some major corruption, political indecisiveness due to constant power struggles, and a demographic crisis (national population loss on an unprecedented scale) and we have a picture of modern Ukraine. I don't think they've had division level exercises systematically in many years. In case of a war, the Ukranians would collapse at the seams, quickly losing control. Not to mention a large part of the armed forces would desert, or even cross over to the Russian side, as a large part of Ukraine is Russian, and another large part is heavily Russified.
The Ukranian Army is a pushover. A house of cards. However, dealing with occupying, and rebuilding, Ukraine afterwards.... especially with a financial crisis, and domestic problems, would be more then Russia can handle. There will not be any war. Most likely some sort of compromise will be reached. Afterwards, when South Stream is complete, Ukraine will be bypassed entirely.