Speculation on what should be, aside, we know that irregular units will be included at least in the SF edition.

I don’t see how a single regiment of irregular infantry will have a great impact on a given battle but it could be very disruptive in the hinterlands of a region and tough to catch. It would demand a much stronger force to catch and defeat it so they would be expensive to counter also.

The reason I say it wouldn’t make much difference on the battle map is that the AI sees all so it is tough to surprise someone who knows there is a unit there.

Against other humans in multiplayer it could be a different matter though.

Irregular units are represented in the game in some form so I guess we will be fighting them in some form.