4Game

You have a stash, character, skills, and hideout system but you go into various maps with a mission and storyline where your PMC tries to escape from Tarkov. The missions can be like rescue your teammate from cultists at night, steal important intel from the Rogues, infiltrate and assault a USEC camp, fight the scav bosses, etc.. You can spawn in with AI teammates who are expendable. You can meet other characters in raid to recruit them. Your hideout can be a straight up scav base where you build it from the ground up and it gives you bonuses and scav soldiers to help you assault a base. Ideally, more weapons, gear, loot would be added to spice up the game. New skills, crafts, faction reputation system, dialogue, and maps. No more online frustrations as well such as cheaters, desync, connection issues, glitches, etc. For the ones who enjoy the game but don't want years of their life expectancy removed from stress, SP would be an enjoyable alternative.

BSG has already shown their desire and ability to make a compelling story from their marketing and Youtube series. There's already a decent amount of interesting background and characters in the game. Incorporating traders into the story as well developing factions and new characters would deepen the lore and overall quality of the game.

Last point is SP could make the Arena mode coming out soon more interesting. Tie in your single player stash with the Arena stash, although with limited items and loadout value to level the playing field. Make gear very easy to craft / loot in the SP end game so you can get a decked out Arena loadout. Might not be everyone's cup of tea since Arena was meant for quick PVP, but it's an idea. For the longevity and completeness of the game, it would be an interesting alternative to the current 6 mo wipe pattern that may get old for a lot of players.