IMHO all apps should install to a location replete with all of their controls and libraries. Yes you would have multiple copies of controls and such but it would be guaranteed that each app would have the correct versions. The need to register them would be removed as each application looks in its own directory for the necessaries.

It sounds archaic and will fill up HD space quicker but with the ballooning volumes this isn't really an issue. Maybe it will assist developers in the art of neat code! Remember when all we had was 64k or less?