Deck-based Perplexicon is... interesting, to say the least. Hmm. I think it would be far too luck based, because a good three-card combo when your opponent has nothing wins the game instantly. "Break held flesh", bam. Limiting cards to weak things would help that, but also makes the game much lower power in general. I kinda wanna try running an IRC game like that, though.
I, personally, don't generally like focus actions in P--the game is better when chaos is the norm. Being able to trade time for reliablity just breaks the spirit in my opinion. I feel similarly about getting bonuses with theme words. People tend to theme anyway, and it's relatively boring play, I'd rather not encourage it. Beyond that, keeping track of what words which people tend to use is a lot of bookkeeping.
I do like the idea of upgrading hexes, or feeding resources from one hex into others. Summoning wood to burn, in order to produce fire words, is a clever and interesting idea. Alternatively, burning a forest to get a whole glut of fire words, but changing production from animals and wood to ash and coal.
"Break held Flesh" seems like it would just cause notable tears and such in whatever body part you held. Plus, there's the roll for it's potency, and you'd have to actually reach melee range and hold on to the body itself, with contested rolls against whoever you're holding, possibly requiring you to get past armor or such. Quite a physical detriment, good chance of being lethal if untreated. I'd say it's balanced.
In that last scenario you mentioned, with the forest burning down, chances are that the total amount of ash and coal words harvestable would be limited to some degree. Once that's all harvested, it's basically plain, possibly haunted land. Oh, Piece, you may want to consider letting a gang destroy/disrupt a Hex rather than claiming it for themselves.
Lastly, I have put a lot of consideration into a card-based Perplexicon, though I would likely have to remove or tone back the Perplex part. It'd be more of a Dexicon, though there wouldn't be a lexicon, either. So never mind the name. Anyway, new players would get a varied deck of cards, each card consisting of one or more words/aspects. To cast a spell, use an amount of cards in your hand, and their aspects make up the spell, and potency is rolled on a d6. Cards with just one word would be named the word itself, and some cards would have multiple aspects and/or an amount of effects, such as "If used with Forward or Sphere, add the other aspect to the spell", "+1 potency to spell if you discard another card in your hand", or "You may add Poison to your spell; if you do, you take a minor wound". Stuff like that. Innately strong aspects, such as Dragon, might have cards with hindering effects, such as "When cast, discard two cards from your hand; if you don't or cannot, this card's aspect becomes Lizard" or "-1 potency to roll". Depending on what your character does/what happens to them, they can get cards based off of it. Additionally, there may be ways to take cards from people/NPCs you defeat, buy/trade them with PC/NPCs, or simply find them in the arena.
Of course, I wouldn't have the skill/confidence to run it for a while.