I'm finishing up the last 150 LF of a 2100F rail job now and we've dealt with the angle points [90 degrees and down] as usual which is to miter the cuts and round off the outside corner with a 36 grit pad after welding. You mention a rounded corner turn you've seen and small elbows for those turns have been brought up. The difficulty with using those, which I considered for this project is the geometry of the lower rail. If you use an elbow on the top rail you would need to use the same radius elbow on any intermediate or lower rails to keep those rails in line with each other or you would have to use two shorter elbows [or cut one in half] on your lower rails to keep them in an equal vertical plane. If you take a minute to visualize this it becomes quite apparant. I discarded the idea for using elbows on the angle points as they created a lot more work and cost and a lot less productivity. The results on the corners meet code and spec. [well not exactly an AWS WPS but no one is complaining] and they look fine, clean, rounded, safe and functional.
All the railing is 1.5" sched. 40 A500 however. If I was doing a stainless railing I might need to experiment with the standard mitered corners/sanding pads and reconsider elbows/bent turns but it would also likely require a redesign of the railings, taking the post out of the x/y corner coordinate and putting in 2 posts offset from the corner to allow for elbow/bent turns.
I use a Dewalt saw with carbide blades [having the best luck with Diablo blades for usage/sharpening and no cracks/loss of teeth] and really don't find the alignment of miters that problematic. Usually just keep the seam on top for reference and a torpedo level to align miters to each other keeps me well within 1/16" of matching vertical planes. A formica sample [grab a handfull on your next trip to Lowes] makes a handy spacing tool for the gap [among their many other adjustment uses] between the miters and tack the corners flat on the table then roll them up to whatever angle of turn is required and fit the notch of the post to the angle point. Most of our angle point turns [all of them actually] also required a change of slope as well.
I'm not sure you will increase productivity using elbows at the corners, they will take more fitting/welding/finishing than miters. If you are tooled correctly, bending the corners could be an option but really precision bends are a challenge. Even Wagner Co. whose products I use extensively have a bend tolerance in their products beyond what I could justify [check me on this but I believe their catalogue states +/- 1degree] which might not sound like much but at 42" [standard guardrail height] is just shy of 3/4" out of alignment and I've found anything beyond 1/4 of a degree becomes visually apparant which, beyond safety concerns, is the ruling considerating for railing work, ie. they have to look right.
BTW another little trick I discovered [won't work on stainless but great for carbon steel] is using nozzle gel for lubricating your hole saws when notching. Removes the need for cleaning prior to welding and does a great job for keeping your hole saws lubed. I use Lennox 1 7/8" for the 1.5" pipe on a Bailiegh TN 250 and get around 125-150 notches per hole saw on the 1.5" [was getting 300 notches per hole saw on the 3/4" pickets and there were 9500 notches needed for that little part of the job]. Also found out my carbide saw sharpening guy could resharpen hole saws for 6 buck a piece and I usually got 2-3 more sharpenings from each one which lowered my cost considerably.
It's been fun, and somewhat profitable, everyone is happy with the work but truthfully I'll be a little glad to see this job finished.