Of course you are not out of place! Feel free to tinker with the cube and improve it any way you see fit! I'm flattered you like it enough to take it as a basis for one of your own.
SPELLS MATTER
I think it's more than possible to extend the archetype to all colours, like you and DBS have done in your cubes. There a couple reasons I haven't:
1) The archetype didn't extend beyond Jeskai until Strixhaven
2) Jeskai Spells Matter is already one of the most common and best archetypes in the cube
3) Most Spells Matters deck are blue decks, which is already one of the top colours in the cube
4) There are already many incentives to pick as many cheap spells as possible
5) Spell matter cards do not crossover with Survival, Pod, Artifacts, Crucible and so on.
6) It was very good stuffy in Temur colours
7) This is the most important one: I am very lazy and it's a lot of work lol
This is why I decided to leave it as a Jeskai archetype. It works, it's fun and it doesn't strike my fancy as much as other archetypes. I'm happy enough with what it does. I also find Memory Lapse frustrating, there are a lot of counterspells I would run over it.
If you want to extend the archetype, I would look into supporting Naya first, then trying other non-blue combinations. Otherwise, you'll have the same blue deck with several different splashes. Start trying Abundant Harvest, Once upon a Time, Berserk and other cheap spells. I haven't done the work here so I can't share you a list of cards beyond that!
GRAVEYARD MATTERS
I'm not the best at working with this archetype so it's a bit wonky. Thankfully, its support cards are great and it ties very well with, well, everything so it works and is fun to play despite my lack of design abilities.
The main issue I have with the archetype is the lack of payoffs in green. You have a lot of them in red, black and blue but green falls behind. This is the issue with Mongrel and its less cool clone: They are enablers, not payoffs. There's three good payoffs and four middling ones:
You can add Wheel of Fortune without problem. I just figured Magus of the Wheel was enough despite running both being a very good option. If you want to try the Mongrels, try both.
Honored Hydra and Champion of Wits are good cards, they are just middling and pretty good-stuffy. I cut Honored Hydra a while ago and never missed it. I think the same could happen with Champion of Wits. The fact is, you have more cards that you know what to do with and neither is that exciting.
STORM
When I first tried storm, I did tun into several drafts in which I had 21 or 22 cards. It should be easier to build a working deck now but the possibility of failure and the fact that I run some good disruption showed me it was very risky. I'm not sure what's the smallest size for a storm deck, though, it might be possible to have it in very few cards.
SPELLS MATTER
I think it's more than possible to extend the archetype to all colours, like you and DBS have done in your cubes. There a couple reasons I haven't:
1) The archetype didn't extend beyond Jeskai until Strixhaven
2) Jeskai Spells Matter is already one of the most common and best archetypes in the cube
3) Most Spells Matters deck are blue decks, which is already one of the top colours in the cube
4) There are already many incentives to pick as many cheap spells as possible
5) Spell matter cards do not crossover with Survival, Pod, Artifacts, Crucible and so on.
6) It was very good stuffy in Temur colours
7) This is the most important one: I am very lazy and it's a lot of work lol
This is why I decided to leave it as a Jeskai archetype. It works, it's fun and it doesn't strike my fancy as much as other archetypes. I'm happy enough with what it does. I also find Memory Lapse frustrating, there are a lot of counterspells I would run over it.
If you want to extend the archetype, I would look into supporting Naya first, then trying other non-blue combinations. Otherwise, you'll have the same blue deck with several different splashes. Start trying Abundant Harvest, Once upon a Time, Berserk and other cheap spells. I haven't done the work here so I can't share you a list of cards beyond that!
GRAVEYARD MATTERS
I'm not the best at working with this archetype so it's a bit wonky. Thankfully, its support cards are great and it ties very well with, well, everything so it works and is fun to play despite my lack of design abilities.
The main issue I have with the archetype is the lack of payoffs in green. You have a lot of them in red, black and blue but green falls behind. This is the issue with Mongrel and its less cool clone: They are enablers, not payoffs. There's three good payoffs and four middling ones:
You can add Wheel of Fortune without problem. I just figured Magus of the Wheel was enough despite running both being a very good option. If you want to try the Mongrels, try both.
Honored Hydra and Champion of Wits are good cards, they are just middling and pretty good-stuffy. I cut Honored Hydra a while ago and never missed it. I think the same could happen with Champion of Wits. The fact is, you have more cards that you know what to do with and neither is that exciting.
STORM
When I first tried storm, I did tun into several drafts in which I had 21 or 22 cards. It should be easier to build a working deck now but the possibility of failure and the fact that I run some good disruption showed me it was very risky. I'm not sure what's the smallest size for a storm deck, though, it might be possible to have it in very few cards.