[tex-live] TL-Announce ?

[Karl Berry]

    would like to know whenever a component that they have installed has
    been updated ?

That is exactly what tlmgr update --list is for.

    Would it not be possible to announce updates at the granularity of
    schemes and collections ?

No.  Every package update changes its containing collection and
scheme(s).

To a first approximation, nearly everything that comes through ctan-ann
results in a package update.  That is the best source of announcements.

karl