Some notes based on my own experience:
* If you can touch type very well in Qwerty already, you may have a much easier time picking up a layout than the average typist. And you may have an easier time retaining more than one layout.
* What you're typing (context) is important with regards to adjusting to a layout. For example, if you learn Colemak and decide to try using the Terminal some time after you've become proficient, you might find it awkward - at first. I personally haven't found the type of physical keyboard you use to matter much with regards to this..
* When I was at the state where I could type in both layouts very poorly (due to muscle memory being confused), I realized I took many things for granted that eliminate needing to type quickly altogether like auto-suggestion/completion - and a lot about software development is about automating tasks.
* When I started to become proficient at Colemak and started to lose my proficiency at Qwerty, I developed a justification and bias that Colemak is way more comfortable for my daily usage.
* The most effort I ever put into typing was ironically typing tests, not programming =P. And those can be really tiring if you do them frequently regardless of layout.
Maybe I find these days that colemak is marginally more comfortable. Maybe I just don't type that much though, although I use the computer a lot. Software developers certainly don't type nearly as much as a "typist job" (if those still exist) in any case. If I lose my ability to type in Colemak, I don't think it will effect me that much. All in all, I can't say my transition was worth my time.