I agree with this, I don't think these suggestions are viable solutions to what we're getting, at least not ones that will please everyone any better than what we're getting.

But I do think there can be improvements to make Blue Mage better than what people are fearing it will be.

I think a lot could be done with this system, even without necessarily changing how it functions to squeeze it into end-game content, in order to make it more viable as end-game ‘relevant’ content for those who would otherwise see it is a “minigame”.

Open access to all content available at its level cap, excluding only the current raid tier. For example, if it were at cap now, then the only content it would be locked out of would be Alphascape, Ridorana, Susaku EX and Ultimate.
It would still be excluded from Duty Finder, however all other content would be possible via Party Finder or otherwise premade parties.

Give end-game relevant rewards for the Masked Carnivale, including:
New mounts, minions, glamour and furniture, similar to the rewards from Eureka.
Current Tombstones, e.g. completing each tier of the Masked Carnivale (there are 25) each day would award you with something like 40 Medacity and 5 Genesis, with a bonus 100 Medacity and 50 Genesis for completing the whole thing.

Give it regular updates:
A new Masked Carnivale stage for each expansion’s worth of content. Heavensward enemies in MC 2.0, Stormblood enemies in MC 3.0, etc. Keeping those rewards mentioned above relevant. Provide more spells with updates, that also increases the level cap, something like:
5.0 increases the cap to 60, and 5 new skills to hunt down.
5.1 introduces the new Masked Carnival up to level 60.
5.3 increases to 70 with 3 new skills and a new level 70 Masked Carnivale.
5.5 increases to the global cap of 80 with 3 final new skills and a new level 80 Masked Carnivale.
This carries on to the next expansion: level 82 with 6.1, 86 with 6.3 and 90 with 6.5, and so on.
Perhaps it would make sense for these new skills to be tied to the raids or dungeons that are unlocked via the level cap increase, for example, learning skills from Bismarck, Ravana and Zurvan in the ‘HW update’, Byakko, Suzaku and Seiryu in the ‘SB update’ etc.

Update the deep dungeons specifically for Blue Mage, with its own rewards for completing them as a Blue Mage. After all, these are things designed to be solo’d so it makes sense that the ‘solo job’ can do them.

Give it a PvP skillset. Every other job has its own PvP skillset that works completely different to its normal skills, there’s no reason why BLU can’t be the same.

Lastly, rename the ‘Limited Job’ concept, it really doesn’t help. How about something like ‘Frontiers’ or ‘Disciples of the Fringe’, given that they’re entirely new concepts that break new ground (at least as far as XIV is concerned) and kind of walk the line between war/magic and hand/land jobs.

None of this would conflict with their vision of Blue Mages being an ability hunting class, that’s overpowered and not balanced for the end-game scene, and I think it would go a long way to alleviating a lot of complaints about it. Not all of them, but enough to make it a ‘success’ for the majority.

Will they do all of this? Maybe not, regular updates might not be so involved and resource intensive, and Deep Dungeons and PvP are totally up in the air. But we can push for it via constructive feedback, and if they see enough people playing Blue Mage they might be more inclined to invest more into it.