Permanent trinket do exist in battle sprites, as Blazecat said. They have even more options to them, such as family damage bonuses and movement speed increases. Pretty huge deal when you can reach max damage and MSI: VH with full black kat and a leveled battle sprite.
And to put it into perspective, I did the math recently. A trinket slot costs five dollars to unlock for a year. That's $10 for 12 months of both trinket slots. That is a fair price for a subscription IMO. If anything I'd like to have larger trinket slot upgrades that come in bulk, meaning instead of $5 for 12 months, it's something like $4.25 or $4 for 12 months of trinket slots. On top of that add the option to buy 1 week slot upgrades, and/or 2 day slot upgrades.
Other trinket suggestions are alright. Usable in both PvE and PvP. I would suggest not having the MSI trinket however, as movement speed is a very powerful asset.
Not using a shield shouldn't be a buff. Shields are an integral part of the game's combat, removing them for a slight boost would just encourage more charge spammers. I don't think many people would give up shield buffs, shield canceling, shield charging, shield bash, and actually defending damage and status for +1 or +2 MSI. Only class that might do that would be bombers, and at that point we should just make a shield that grants bomb MSI: med.
Sniper gun, ehh... Magnus lines do this pretty well. If the range gets too extreme then it leaves you out of the combat too much.
No-charge bombs would be nice. A standard attack for bombers in general is long overdue. Dropping a smaller radius, less damaging bomb would encourage pretty interesting attack styles.
Armor revamp in general would be nice. Stronger offensive gear would lose health, weaker but defensive gear would gain health. That'd be a good start to make tanks be able to well, tank damage.
1. Permanent trinket slot exists in the form of a Battle Sprite. It may be small but it'll get better.
2. Some sprites have ultimate abilities that do buffs. Like the Seraphynx, which can give Shield Regen or CTR.
3. Maybe if you removed the shield, you could use the Shield button to walk in case there's something you really need to dodge.
4i. Pulsar Line is considered to be the snipers of this game, which deal more damage at a range of 5-8 blocks.
4ii. Bombers are forced to deal with walking slower when planting bombs, you can't do no-charge bombs. Plus, Nitronome has a pretty big area.
4iii. Tanky armors really do suck. They don't protect from Ranged Attacks and reduce your evading skill. They need some work.