8-bit Computer TV Channel Use

Assuming that I don't find an off-the-shelf converter that Just Works for our poorly-behaving vintage computer video outputs, what I have in mind is this: A converter that is specifically designed to emulate the response of an 80's TV or 80's composite monitor when driven by a vintage computer output, and translate that as well as practical to modern displays (particularly, 1080p via HDMI). I have some ideas about how to accomplish this, but I will need to do more work to see if I can create a solution that is not absurdly expensive. On the input side, I envision having two RCA jacks and an F connector, accepting composite video, Y/C separated video (for C64, etc.), or TV RF input. It should be able to accept NTSC or PAL, so the US and UK folks can play. Is there a need for SECAM, or any other video standards? What about other electrical interface options? I'm only hands-on familiar with US machines. I understand that Atari computers were especially popular in Poland, so I'd like to support those... anybody here know what format/channel a Polish Atari 8-bit would output? In the middle will be some FPGA to perform any necessary magic. I've been looking at a prohibitively expensive ($115) one that has enough dual-port RAM blocks to support a frame buffer. I need to see if I can push the frame buffer out into external RAM in order to move to a cheaper FPGA. It would be ideal if the video parameters could be figure out automagically, but I have a feeling there will be a need for user-adjusted parameters, and possibly even loading up different FPGA programming to handle some odd-ball signal. Output would be HDMI, at 1080p. Are other interfaces and/or resolutions desirable? I'd like to keep it as feature-simple as practical. Handling the VHF/UHF tuner economically may be another sticky point. Maxim makes a tuner chip that's available at Digi-Key, but I refuse to design Maxim parts into anything on account of off-topic reasons. Mouser has stock of a very inexpensive ST tuner chip that looks very promising, but the full datasheet isn't openly available. I need to contact ST to see if I can talk them out of it. Their site mentions an NDA for the eval board, so it might be tough, particularly since my intention would be for my design to be open to allow off-label uses. Assuming I don't lose interest before completing this (a high-risk caveat, naturally) and that I can find a way to make the price bearable, what do y'all think about this silliness? I'm particularly interested in learning about non-US TV formats so I can design in maximum utility.