I bet Christian yoga will eventually become really popular in the US. I'd imagine it would keep the physical elements of yoga but infuse light Christian meditation into it, rather than the vague eastern spirituality that's currently everywhere in the industry.
What I'm saying is that I think there's an untapped market of people in the US that would be more likely to commit to regular yoga if the spiritual component adopted traditions from Christian meditation. This is based on discussions I've had with family and friends that say they mostly enjoy yoga but find the spirituality component or 'a little silly,' off-putting, or distracting.
Many US yoga studios and instructors are not dogmatic and are quite experimental and creative in their craft. There are already a number of relatively popular disciplines that de-emphasize the spirituality and focus on the fitness component (i.e. power yoga). My belief is that as yoga continues to evolve and grow in popularity in the US, some studios will reintroduce the spirituality component by fusing traditional and Christian beliefs, and that these studios will succeed in reaching a broader audience.
It's less easy to quantify your progress than with weight lifting (whose easy conversion into numeric growth I wonder isn't one of its attractions when you're a data-driven kind of person) but has further reaching benefits beyond basic physical strength.
After 3 years of fairly regular yoga practise (3-4 sessions a week), even when combined with a fairly poor diet/lifestyle alongside it (way too much fun), left me feeling stronger, fitter, calmer, more centred, more energised* than I ever had before.
For those of you who, like me, are put off by the more 'hippy' aspects, I'd say it's a question of finding the right teacher rather than writing off the entire practice (my teacher at the time was nicknamed 'El Sargento' for her, shall we say 'strict' approach -- she taught Iyengar yoga with is a lot about details. This didn't suit everyone but suited me down to a tee).
There is an awful lot of pseudo religious bollocks that surrounds it but within that there's a really solid method for improving the quality of your life.
* https://www.youtube.com/watch?v=laoq1eeIUxQ