from a teams perspective, why would you invest high dollars in a running back? They are the easiest of the skill position players to replace... it just doesn't, or rarely if you prefer, happen anymore...
and if you need to put a qualifier of a 2000 yard season on Jonathan Taylor, come on Fam ... that's a HUGE if assumption on your part... but say he does, whats going to happen? as you said, age and use devalue a back... a 2000 yard season for a back means averaging 117 yards per game... based on his 5 ypc career average, that's 23.5 carries a game at 5 yards per clip... project that out and its 400 carries for Taylor... (and lets not forget no back has ever achieved the 2000 yard season twice in their career)...
But if he manages it, most likely the colts will tag him... in doing so, it will increase the overall cap values for the rb group under the cba, making it just that much easier for the next guy to earn a bit more...