Having finally bitten the bullet and upgraded to 5.2.1a, I offer a few random first thoughts:
Pretty obvious, but maybe worth saying; if you load a layout created under an earlier version into 5.2, amend it and save it, your earlier version will not subsequently be able to load it. So if for any reason you think you might want to revert to the earlier software version, you need to save the 5.2 file under a different name.
Easements: now you've implemented cornu curves, does anyone use the sharp/normal/broad easement options? For the way I work, the ability to just toggle Cornu on or off (where "off" is the current "none") would be much more effective.
Rotate: It would be excellent if, after selecting an object and right-clicking for the context menu, you could immediately see the right arrow against rotate and use it to bring up the rotate options. As it is, after selecting rotate, either via the button or the context menu, you have to shift right-click and then mouse over rotate in the context menu to see the options. This is clunkier than in v 5.1 where all you had to do was select rotate (either way) and then shift-right click to bring up the options. I assume this may be fairly easily do-able, as there are already right arrows against other commands when you first see the context menu.
Bridges: An excellent addition, though I suspect this may not be easilydo-able ..... it would be good if on selecting parallel tracks to be "bridged", the result was a single bridge instead of two parallel bridges.
More power to your programming elbows, and thanks for all your efforts!