It would be much easier to learn how to encode videos properly than it would be to make a ROM like you are suggesting.
Is there much to learn there?
When scaling video up to screen's native resolution make sure to use nearest neighbour method (might not be an option for premiere if you are lumped with modern adobe if a quick search just now was anything to go by, sometimes goes by other names in other programs -- avisynth for instance calls it pointresize http://avisynth.nl/index.php/Resize#PointResize
). Make sure to multiply by a whole number to whatever is at or under the resolution of your final video.
At this point either overlay the video on a plain black (or slightly off black if you prefer that CRT/RF glow effect) or add borders to the image to make it up to resolution (overlay might be more CPU intensive, borders more annoying to do if going between various systems and regions thereof).
If you really want and as it is current space year then most screens around will be 16:9 or worse then with overlay you could also do a border matching the game/system (think supergameboy or various emulators) or that effect some things like to do where they blow up the video in question, blur the background a bit, desaturate it and call that the background with the main even being overlayed on top of that (possibly with some borders depending upon the thing you are going for).
Never been a fan of scanlines myself (my background as a filthy PAL viewer perhaps) but they are also easy enough to add with most things. http://avisynth.nl/index.php/Scanlines
as I do like avisynth (especially if you have dozens of clips and might want to replicate an effect on all of them).
If we also get to replicate http://bogost.com/games/a_television_simulator/
then that gets harder but at the same time crt filters are available for many systems these days (maybe not with all the emulators but enough).
Wind the video onto something like a raspberry pi with https://www.screenly.io/ose/
on it and you can either pick and choose/add new things as you make new ones, lose logos or segments if they bore you and go from there, or make one megavideo and just have that loop.