PS: Could be some of the stuff is allready in the game, I haven't paid much attention lately. Also I don't count what mods do because I want official support / addition for the stuff.
- Costum Logos for your unit. Just make a folder where we can drop PNGs
- Costum Paintjob or at least costum colors for your Dropship
- Different Dropships with different capabilities. More mechbays, faster repairs, better med stations...
- Unique pilots for hire that have their own voicelinces and looks
- More command options in the field like chageing formations, ordining units via the battlegrid
- Option to give general instructions to the AI before a drop. For example "Stay at 150m of the enemy", "circle enemys", "use hit & run", "keep out of sight and use indirect LRM fire".
- New Storyline Campaing like Kestral Lancers but with more cinematics (you can do it

- Reworking of Tanks. Make them a tad weaker but let them move in groups AND in formation.
Let them create firing lines or place them dug in. There should be at least 3-5 tanks per group.
That would also mean to reduce their random appearances on the maps. Let them either guard importend targets or if the roam around, let it just be one, maybe two groups not more.
Basicly tread them more like a mech.
- Let us meet/fight other famous Merc or House Units
- Some more physics gameplay like places with destructable terrain like overhanging cliffs, bridges, building that fall to the side, smashing your enemys...or lancemates.
(And a fun mode where we do Union-Dropship-Bownling. Shoot away the landing struts and see it roll away... just kidding, don't do that

- If not allready done, every tech that came up before the Clan invasion. IIRC some stuff that was discovered by the Grey Death Legion was allready showing up before the invasion.
- Clan invasion ... difficulte topic because I think it should be a very one sided battle at the beginning of a big story DLC that slowly turns around with new tech but then...who likes getting his *** handed over in a game. Even if you know you will beat them later on.
Still could be an interesting experiance from just trying to reduce your losses while fighting alongside other merc units or house units, constantly falling back to slowly get a foothold, new tech, new mechs and finaly turn things around.
Storywise I see potential but you need a good writer and lots of hand crafted missions.
On the technical side you would need to implement something like the Batchall system, new AI that follows Clan doctrines. Options for players how to exploit those systems like the IS did. Like using traps, hit and run tactics and other dihonorable tactics. Except you where Draconis Combine warriors...then you just get your *** handed over because honor

I mean it could be fun for you to choose between accepting a batchall to reduce your units losses or do you go "**** you I go all in" and hope you get out on top? Maybe you know the battlefield well enough to plan a trap?