Once a spell added to the spellement list, it's not tc pre-enchantable
Unless it currently exists in the bazaar/library you can't create tc's of any card that is on the spell writing list. You can enchant a spell card that is in your main deck, but it never becomes a tc variant. Since I don't have spellementized cards, i do have the originals spells, Can I enchant spellementized card that exist in my main hand, like I can the originals?. Like add primordial or gargantuan to spellementized leprechaun?. Since I have not gotten around to making any spellements except daybreaker, nightbringer, Can you sun enchant then in you hand, I.e. primordial or gargantuan + leprechaun(spellement)?. As they add new ones to the spellement list that will restrict making tc’s of them also. I like tc sun enchanting the originals, but at this time that is impossible. What happens if firedragon, meteor, etc, gets on that list. It forces you to keep them in your main deck. Not good for medulla fights. wish KI would make spellements a new class of spells, leave the originals alone.
Re: Once a spell added to the spellement list, it's not tc pre-enchantable
Yes, it's unfortunate to lose the ability to make TCs the way we used to, though the spellemental improved versions have their own rewards. Trade-offs I suppose.
I believe the concern was that TCs of improved spells would be OP, especially for PvP. I like your idea of keeping the original accessible for card enchants.