The Side Initiative variant in the DMG (pg 270) states that both sides in a combat roll a d20 for initiative with no modifiers. I think the stated exclusion of modifiers was primarily for simplification purposes, but I also think it screws players whom have bonuses to their initiative score for various reason.
I had a few thoughts on adjudicating this in some manner, but what seemed to be the fairest would be to determine the average initiative bonus for the group and apply that as a modifier. For example, assume the following group members all have a base Dex modifier of +2, their initiative is as follows:
- 10th level Barbarian - +7 (gets a +5 bonus due to Advantage from Feral Instinct)
- 10th level Bard - +4 (gets 1/2 proficiency bonus from Jack of All Trades)
- 10th level Fighter - +12 (has a Blade of Warning and has taken the Alert feat)
- 10th level Monk - +2
Overall, this group has a total initiative bonus of +25, which when divided by all of them is +6 (rounded down).
Is this a fair way to adjudicate the side initiative roll or is it unbalancing to do in this manner?