Something like this would require a major hardware redesign (and a significant increase in cost), since, as I understand it, the current design of the OSSC does not include the requisite memory for the kind of framebuffer required for things like framerate conversion and scaling. (We’re talking PAL-spec resolution and framerate; but, it’s RGBHV, not actually PAL, so there’d be no need to decode anything.)
In the meantime, if this is something you want to address much sooner than an OSSC 2 (which may never come), there are some workarounds to having this functionality built into the OSSC.
The best option, in my opinion, is to get a new display that supports 50Hz sources. If you’re in the US, like me, it can be quite a pain to find something that supports 50Hz, being that it was mainly used in PAL regions, and there was no real availability here. That said, contemporary 4K TVs tend to have a wide support for resolutions and refresh rates, and, even though it may not be advertised in the manual, there may be reasonable TVs that do actually support 50Hz; you’ll have to ask the manufacturer and/or bring your Amiga in to a store to see which TVs support 50Hz (and maybe check the configuration menus to see if 50Hz is a togglable option).
Failing that, framerate conversion is on the table. If you don’t want to go the Framemeister route, you can pick up an Extron IN1508 cheeeap on eBay. It’s a presentation scaler and seamless switcher that can take the RGBHV directly from the Amiga, auto-detect the video mode, and spit it out at your choice of format (RGBHV, RGBS, RGsB, YPbPr) and resolution (up to 1080p and 1600×1200).
As bonuses, it has a low-pass filter, it supports switching stereo audio over RCA (whereas most Extron equipment uses the exotic Phoenix/screw terminal connectors), and any mode switching should be seamless. Of course, there are tradeoffs: it doesn’t handle 240p (always deinterlaces 15kHz); and the scaler cannot be disabled (because that’s what it was designed to do), so there will always be a small amount of lag.