Great interview with Rub!
Next two things this game needs is Melee and Prussia, population-wise I think that is what is most important.
The competitive-side of HoldFast consists of the Conquest Leagues (which are currently on Hiatus) and Line Battle 1 v 1's that regiments organize amongst themselves.
As far as the Conquest Leagues go, having a variety of small-scale maps to choose from would be great, we're limited to only a couple at the moment.
As far as LB's go, I think a League would need to be formed with uniform rules & regulations so regiments could be ranked and progress as they participate in matches against other regiments. There is no real sense of progression if regiments are left organizing 1 v 1's amongst themselves.
And of course, the two features mentioned above (Fixed Melee, Prussia) would absolutely need to happen in order to stimulate the HF playerbase and so players can have a more enjoyable experience.
Customization is silly, but that's just my opinion.