I'd like to see more original skin lines to be honest. That's not to say I don't want to see additions to existing ones, but there's just so many that already have so many (close to, if not a dozen or more) that the overall variety feels less somehow. If it's addition to an existing skin line, I would rather then see lesser touched ones. Some only have a handful, and/or haven't been visited in years.
Things like Pool Party, Project, Blood Moon, Arcade/Battle Boss, Star Guardian, Dark Star/Cosmic (I know they are technically different lines but they seem visually close enough to be the same), etc., are all getting to be very big skin lines and it's almost a given to get their yearly or bi-yearly additions.
As for champions...
There's the obvious few that just don't have many (Worlds team skins I don't count); Zac, Kalista, and Orrn, for a few examples. I'd be happy to see Riot trying to bring more parity (though i understand it will never be perfect parity) rather than adding to what already has a lot.
There's the other obvious few that haven't recieved one in forever, like Skarner, Xerath, and Mordekaiser (Shaco until recently).
As a biased choice, Mordekaiser. His last skin was released in 2015, and prior to his rework, almost half of the offerings were mere chromas, making his skin count deceptive when it wasn't even high for how long he's been released anyway. Like Morgana, his rework left things to be desired with a few skins, and NONE of his skins are even above a 975 cost/quality; he doesn't even have anything as good as a Epic skin let alone a Legendary skin. Due to how long it's been and how he has no high cost/quality ones, I do think it's only a matter of time now, but I'll be honest; I'd like to see him get more than the one and done 1350/Epic or something for three or more years that I think will be the case. Given his skin count to years released ratio, I'd like to see two or three in around as many years, but I'm not not holding my breath. I'd love to see him get an Ultimate skin, and ever since the community thought he might possibly get it back when Udyr did instead, I've thought of what it could be like, but again... I'm not holding my breath. At this point, a Legendary "God-King-alike" (but not necessarily that skin line) would make me happy enough.
Would also be happy to see some for Neeko and Sylas (somewhat new-ish, but either no or one skin only outside release skin), and also for Volibear or Trundle, as I like those two and count/time since last is a bit low as well.
