It won't happen, unfortunately.
It is the nature of software that its installer has to have intimate knowledge of the components being installed, knowledge that is specific to one package and one vendor's practices. Even if all vendors could be convinced to adhere to a standard, there will always be some product-specific, host-specific and platform-specific differences. Even for a single product, there are different conventions between Macs, Windows and Linux systems for where components are stored and how they are handled by the O/S.
Of course, you could have a common installer that establishes firm standards that all participating vendors are required to adhere to, and that was smart enough to support scripted rules for when exceptions to those standards are unavoidable. However, such a utility would require ongoing maintenance and support, and would therefore be a
commercial service that vendors - and ultimately their customers - have to pay for.
Look at how many Kontakt library vendors opt out of Native Instruments registration, even though there are benefits to both vendors (piracy protection) and users (convenient updates via Native Access). It's because of cost that vendors eschew that service. I know I don't want to pay an extra hundred bucks for a product just to make updates more convenient.
A more probable scenario would be to let each vendor create his own installer, but to convince them to conform to some agreed-upon UI. That way, you can hide complexity and proprietary elements behind a familiar, friendly user interface. Meldaproduction, Cakewalk and Native Instruments already have very good multi-product installers that could serve as a universal model. This falls way short of the ideal expressed by the OP, e.g. a one-click update for everything, but it'd be a step in the right direction.