I have issues with these, personally.
But to elaborate on some of the particularly bad parts:
The timer would clash directly against XIV's instance design. XIV's instance timers are very forgiving, and there's no cost for failure but "wasted" time. You keep food buffs through death, cooldowns reset, etc - Everything about the game encourages you to keep on trying, keep on pushing til you get there. Making it 90% through a dungeon then getting kicked out or auto-failed due to the timer just doesn't fit.
In the same vein - Key bricking is an utterly repulsive idea. The idea that something actively discourages you from playing the game (Because you or someone in your group might play badly, and you'll be punished with a downgraded keystone) is baffling to me. Again, generally XIV's design is that you waste nothing but time (and a pittance of gil in repair costs) for failing, so you're always encouraged to keep trying.
Keystones at all, really. Instead of forcing people into certain dungeons in order to progress your key, put gear with different substats behind different dungeons.
As an example, Dungeon A drops Crit+Det earrings, helmet, and bracelets, but Ten/Pie/DH+SkS/SpS gloves and boots, while Dungeon B drops Crit+Det gloves, rings, and necklaces, etc.
This way if you want a full set with optimal stats, you'll naturally run each different dungeon because it has the loot you want, rather than because word of god demands that you will play X dungeon now if you want to keep progressing. Alternatively, the casual player that doesn't care as much for optimisation will be able to play whichever dungeons they like.
Grinding up your key level each week instead of just picking the difficulty you want to play is a needless waste of time.
Seasonal affixes artificially created FOMO. You can never go back and play BFA dungeons with BFA affixes. Hell you can never go back and do BFA M+ at all, but that's another topic. In a lesser sense the same is true of a weekly rotation of affixes, they should either be chosen as part of picking a difficulty level or randomised upon entry.
With all of this in mind I don't think any incarnation of Mythic+ in FFXIV would be acceptable unless it only vaguely resembled the core concept of "Dungeons, but with scaling difficulty".