I remember reading a news about Samsung selling an 'Evolution Kit', which would implement next-level standards on older sets, to customers.
Yes - at one point Samsung sold very slim, premium LCD TVs with a single power+video cable from a second box that handled tuning, HDMI switching etc. duties. I think the aim was for that second box to be upgradeable/replaceable whilst you kept the same display on the wall.
However the major developments that have driven replacement TVs have been display rather than source related (Full HD->4K, SDR->HDR etc.) so that concept probably died a death.
I think there should be a global standard for such kit, so the customers can update their TVs to the latest standard without having to buy a new set, regardless of manufacturers.
I think that the market for that is kind of covered by third party set top boxes like Apple TV 4K, Amazon Fire TV stick, Roku Streaming Stick etc. - you replace those rather than your TV if you want to upgrade your online connectivity ? Or do you mean a way of replacing MHEG5 with HbbTV in the field ? I doubt that kind of thing will happen - as the timescales for those kind of upgrades are once every 10 years or more - which is 'replacement TV' territory.