I'd say jump into the pool. Gear devalues over time, bodies more so than lenses... but if you get a 6d for 1500 now and a 50 f1.2, that would go a long way in getting you close to where you want to be. Then when the time comes, sell the 6d, decide on the lens... it can be cheaper than a rental.
When I got my Canon xs, I paid about 400 plus two lenses. Two years later I sold all of the great for what I originally paid. Fast forward to my 60d and after two years I lost 150-200 in value... still pretty cheap for a two year rental.