First off, Lyrion, you totally ignored the part where Gargos was saying charging up the speed of the blob. By saying "this was in the previous test," you totally misrepresented the previous patch's charge mechanic: slightly increasing damage.
Secondly, Gargos, I will say I'm pretty against making concs chargeable in any form. The brief test of chargeable concs felt extremely awkward to use, even tap-firing felt... gunky, because the exact length of your tap would affect the timing of the shot. Having the speed of the shot vary based on charge would make it unnecessarily difficult to use, since each slightly different charge level would affect the amount you needed to lead. I think that's gross.
Thirdly, if a charge mechanic WERE implemented, I think it should be implemented in a way that makes tap-firing simply impossible. For example, concs could require a minimum amount of charging before they could be fired at all, and after this minimum amount of charging was achieved, you could hold the charge for, say, five seconds.
I don't really want this though, I like the current beta implementation where it's tap-fireable but only knocks down running/jumping people, staggering otherwise. It's like Push, for gunners. It seems reasonable and like it has reasonable counterplay.
(Another joke idea I would want for conc would be... basically the idea I described above, except that after five more seconds of charging the shot would instead be a Concussion Rifle shot. A big area blast. This would be very silly.)
(A less joking idea for conc would be that there would be no charge mechanic, instead the shot would simply fire... say... 500ms AFTER you press the button. As in, there would be sort of a "wind-up" to the attack. Like an automatic chargeup. This would give the target a moment of warning to try to evade.)