"This Pokémon needs a mega" is also one of my least favourite phrases
Especially since any Pokemon that doesn't have a Mega is just as deserving/qualified of a Mega as the next. What makes the Pokemon that person pointing out so special that it should be on the list above others? The only Pokemon (that we know) who would have any priority to get a Mega would be Flygon since GF said they were planning on giving it a Mega but couldn't think of a design in time. So while other Pokemon are begging for a Mega, Flygon is the only one who's going "so did you think of anything yet?".
"Megas should be removed" is one of my least favourites phrases because GF/Nintendo will never remove them, whether we want them gone or not.
Don't see why they would want it to be removed. Okay, maybe because they feel like they're forced to use a Mega to be competitive... but then again when haven't you been forced to use a certain Pokemon or strategy to be competitive? Also, sure while some Pokemon already competitive get Mega to make them even more powerful, Mega gives a chance to Pokemon which aren't a chance to play in the big leagues.
I would be more worried about, from the success of Mega Evolutions, of GF adding in another form transformation mechanic; mainly the one the anime introduced because Ash just has to be a special flower instead of wising up and getting a Mega he and Greninja instead get their very own power-up transformation. This would draw work on more Megas and I'd prefer GF to work on a new mechanic they introduced than putting it on a shelf (they have a habit of doing that, like a child playing with a new toy but forgetting it when something new comes along).
Kurona needs a Mega
I actually think, aside from wanting Mega Flygon and a few more Gen V Megas, I think we're good with Gamefreak surprising us with ridiculously random Megas (like seriously, Beedrill?)
Don't forget Gen VI (and VII) Megas (unless they want to ignore giving new gen Pokemon a Mega which I can understand).
As for surprising Megas, I would say there's still a few. Actually, it's not really the Pokemon itself but the mechanic associated with certain Pokemon. Ditto, Pokemon with Formes, Zoroark, Pokemon with major gender differences, etc.. Also who knows what direction they may go with a Mega. Would they go the obvious or would they pull a twist? Though if your standard for "random" Mega is Beedrill there's a ton similar Pokemon I can mention on its level.
The only things I could really see as a Mega being necessary for is Starters to keep things equal, but even then it's pretty arbitrary.
Starters will most likely get their Megas in their remakes. That leaves the Gen 2 Starters in a tricky spot though.
If Gen VI is anything to go by they might buff non-new Starters until they have no more. If I were to make a prediction:
Gen VII: Sun & Moon will have the Johto Starters. There will be no remake as we're still on the 3DS which has ORAS. Alola's "third version" might give Alola Starters Megas. They may also do the Johto Legendaries at this time as well.
Gen VIII: First pair games will have the Kalos Starters. A new handheld will probably be out by then so there will be a Sinnoh Remake for their starters. This gen's "third" version will give their Starter's Mega.
Gen VIX: If it's on the same handheld as Gen VIII than it'll have the Unova Starters. If not they'll save the Unova Starters for the Unova Remake.
Of course, this is just assumptions based on their current model. For all we know they may decide to release a Gen I, Gen II, or maybe a Kanto + Johto game and that's when they'll do the Johto Starters and Sun & Moon will have the Unova or Kalos Starters. Or since Sinnoh, Unova, and Kalos remakes would be in the future they'll save their Stater's Mega until then, playing the long game (and thus giving other Pokemon a chance to have Megas).