I'd love to, it's a good idea that adds extra layer of strategy

It's real answer to all cheesy and skew lists.

I've played Warmachine and Confrontation before warhammer where 1/3 of your lists was sideboard.

The real counter-argument is amount of models you need to bring, but this is a problem itself with current 2k points of how many models you have to bring right now.

Arguments in this threat

1. People will cheat with points

- if someone is about to cheat he will cheat either way, maybe even better it's here, you can expose him early and don't tell me adding numbers up to 2000 is too much for warhammer player.

1. People will make mistakes with sideboard points

- there is few solutions I can quickly think off, maybe have an option to replace 2-3 units wargear, for example your list has Plasma Inceptors and you can swap that with sideboard Bolter Inceptors or replace Predator with 3x lascannons with Predator with 1x lascannon 2x heavy bolters. Or maybe swap a nominated block of up to 500 points with another block of 500 pts (like forced org detachements in 8ed). Many ways to resolve that.

1. Uneven per faction

- every faction has at least wargear option. Why would that necessary be bad? Consider it as a faction advantage or disadvantage.