How about this:
Remove most items from the shop, leave only "standard" items. Each nation will have only a single weapon in strength class and weapon type:
a single 1h weapon for 9 str
single 1h for 12 str
single 1h for 15 str, and so on
single 2h for 12 str
single 2h for 15 str, so on, you get the point
Same with ranged weapons, ammo, horses, armour, everything. Only the most common weapons stay. All other items are
luxury custom items. How you get them?
These items have various rarity, so most desirable weapons have lowest drop chance, crappy stuff which no one uses is the most common. Ultra rare stuff like boulder on a stick might be there too.
To give players more incentive to hunt for those loot boxes and use previously unused "crappy" common items, maybe buff the non-standard, shop-unavailable items by a little bit.
But why this? Regular grind is tedious and boring, especially if you calculate how much time you need to spend to get to the next item, level, loom, whatever.
Look at all the top games on Steam:
CURRENT PLAYERS PEAK TODAY GAME
923,097 1,000,447 Dota 2
673,072 905,755 PLAYERUNKNOWN'S BATTLEGROUNDS
611,925 632,524 Counter-Strike: Global Offensive
100,941 117,107 Tom Clancy's Rainbow Six Siege
What do they have in common? That's right - some kind of random drops at the end of a match. Why do people like this? I don't know, but
Of course, it would also require a wipe since people have all the stuff they want anyway. Also, you can make drop rate scale with player score - so well performing players have a good chance to get items, trolls and delayers will remain with common gear for a long time. I think it's better motivation than multiplicator. Forever long wait divided by half is still forever long. But if your drop rate is twice us much, boy o boy I wonder what cool weapon will I get!
tl;dr wipe and loot boxes instead of grind