Julian,
(edit: I crossed with PPRuNe Radar's post above...)
In my experience, ATCOs would not all be individually invited to comment on such future proposals or projects. If so, then we'd all be overwhelmed with such invitations.
However, I'd expect at units where the discussed change would have an impact on operations then the units' Ops section (consisting of ATCOs themselves, of course, amongst others) would be involved, and in the course of that process, 'coal face' ATCO would be canvassed for their opinion.
At the moment the views from ATCOs seem to be unheard as they are not allowed or seem not to want to comment where their views may be seen on public viewable response documents because of their employer.
I'd wager that there are few comments because to ATCOs, the proposed change (as much as I understand it), will not impact on them very much at all. Bear in mind of course that an ATCO saying 'we don't see a need for it' is very different to 'it's a bad idea, we shouldn't do it'.