My biggest problem with invasions are the story aspects. Why is this particularly world being targeted? Why are we attacking it? How do we ensure that the world falls / doesn't fall into enemy hands?
I'll use the Republic as an example. One Sith are invading them, Mandalorians are joining in as hired mercs and you add the odd Primeval / Dark Jedi / Sith Lords normally unaffiliated with the OS but joining in the invasion because the Republic losing another world fits in with mutual interests. The first two questions are minor (and don't really fit in with this example) but I'll try and fit it in with story telling. Why hasn't the Republic tried to blockade it's space? It has the ships and personnel. In fact, a lot of the roleplay that the Republic has done is the development of it's military and tech, much to the dismay of many Jedi. Why doesn't it use it to stop further attacks? Surely a blockade in place would require the enemy to first bypass it in one thread. It gives better leverage on the negotiation table, when the OS (or any other faction) wants to invade.
Another thing. Skirmishes. The concept of skirmishes has become lost in the past year. I can't remember the last time I participated in a good skirmish. I think it was when the Obscurity fought the Chimaera somewhere near New Order space, when the New Order was a thing. That was 2014, so it might be longer, at least for me. Why don't the One Sith launch several skirmishes, to take out key leaders- key Jedi, military personnel etc.- to make the next annexation of a Republic world easier? Why don't the Jedi / Republic do the same, only in reverse?
The rebellions were a good start. I saw points made against Republic writers who didn't enjoy the fact that any of their dominions could be rebelled and possibly lost because the enemy can now come in and legitimately sustain the pressure on the faction. But skirmishes? They've become lost and with them has the storyline. Why can't we, as a community, come together with the 100+ or so characters and conduct a really nice battle, that has some repercussions for the winner or losers, without necessarily ending with a star system becoming annexed by the invading force?
Battles create stories. The Battle of the Kaliida Nebula in the Clone Wars was a great episode. It expanded the Clone Wars and the story. Gave it depth. We're missing depth in these invasions. I thought it was fantastic that the One Sith could come out of no where and shrek Coruscant from the Republic- the #1 faction at the time- in some heavy Sith orientated revenge due to what the Republic did to them in the 830s. But what was the story after that? I haven't a clue and I've participated in the majority of invasions- on both sides- since the gecko.
I hope this gave some ideas.