To me it seems outright impossible to add spell creation to this game because the main magic system seem to be completely different than what we had before.
Spellcombinations, maybe, but I highly doubt that too...
As for the extra weapons, it's about being unique, I mean adding spears as just another two-handed weapon that just looks different is pointless. Like crossbows, they work differently than bows.
You're actually wrong. Spellmaking is indeed very possible. You see many effects of spellmaking in the game already, any person who has taken the "Extra Effect" perk in Enchanting has experienced the fundamental aspect of spellmaking.
The biggest hurdles probably come from how a custom spell plays into leveling a skill, when it's multiple schools, and how to combine delivery methods. It's fairly easy to say "Let's make a fire spell that gouts for 80 damage per second" but it's a lot harder to say "Let's make a flame gout spell that shoots ice spikes and also frenzies nearby enemies with paralysis runes".
So it gets complicated, but I believe it's possible. I highly doubt it'll be the same level as the simple system in Morrowind and Oblivion, likely you can only combine like delivery methods, but it's better than sticking with an 8damage per second frostbite spell for 80 levels.