Most people hang on to their TV for 10 years or way more than that. Expecting people to have truly modern TVs is a crapshoot. Only enthusiasts upgrade to the latest and greatest.
And unless you're a very informed technical savvy consumer who does his research and knows what he's buying, upgrading your TV might end up being a downgrade for you as you could end up replacing a perfectly good dumb TV with a new WiFi "smart" TV that spies on you and serves you ads.
Unlikely. I doubt that state of the art video processing is available in hardware. There are custom finetuned neural upscalers and frame interpolators available for every kind of content.
Usually software designed explicitly for the hardware where it runs, while OS software is designed to run on general hardware. If there is hardware specific fixes, they might be skipped as it'll make compatibility worse while software designed for exact hardware doesn't make tradeoffs like that at all.