1-We will likely see more moveset changes...:
As stated by Serebii himself, all third games of each generaion featured moveset changes(which is inaccurate, by the way, Emerald's only true change was the addition of Volt Tackle, whereas most of the changes in FR/LG were not trasferred over as Emerald reused movesets from Ruby/Sapphire, and since it was the last game of the generation, the lack of changes remained dominant). However, most sequels and remakes featured moveset changes, but only HG/SS and B2/W2 contained major intergenerational changes, the latter because of the expanded and heavily marketed New Unova Dex(with few additions to TMs on Pokémon with low movepools).
As for the former, though it is partially the HG/SS' Johto and Kanto Pokémon to the next generation, it was also to boost the anemic Egg Move movesets of the Gen IV Pokémon.
However, expecting massive moveset changes would be optimistic for three reasons;
1-Masuda is confident in X/Y's balance.
2-As the Pokédex is already gigantic and since most Pokémon already got a update in some form, there is little remaining to add, at least on paper(of course, this is completely false, as most Pokémon are far from being optimized moveset-wise, even Smeargle who can't learn Chatter in spite of the lack of the banworthy voice recording gimmick).
3-The amount of Move Tutors will surely reach near 70-80 moves, making them essentially a secondary set of TMs.
However, many of the Egg Moves' of the Gen VI Pokémon are abysmal both number and quality-wise, and many of the newly established and existing chains are not fully utilized yet. As such, it is almost certain that we will see updates on them, at least if this generation is long enough to host three sets of games.
There are also a few errors that need to be fixed, such as Spinda's inability to get Sleep Talk and Venipede's second Venoshock which likely should have been Venom Drench.
2-There will be more periodic rematches and more opportunities to encounter existing battle methods:
This is also a no brainer and a common occurance for later generation games, as a larger cast would also mean more periodic battles, and a larger region would mean more horde encounters. However, there will likely be more Sky Battles as well(which would also be a direct result of a larger region, but whatever). Inverse Battles are unlikely to get more attention unless they are actually marketed.
3-There will be more alternate mini-games/quests:
This is also well known for HG/SS and B2/W2, but FR/LG and Platinum both had various multiplayer mini-games, either through Joyful Game Corner or Wi-Fi Plaza. A similar thing is seen with Xtransceiver mini-games in B2/W2 and their ability to be used over Internet.
4-There will be new connection features:
But it is impossible to speculate what they might be.
5-There will be additional mini-games on PokéMileage Club for the releases:
Though this happened for B2/W2, the reasons for that were different. In B2/W2 the changes for previously unavailable Hidden Abilities. But for this generation, the changes will likely be for currently unreleased or single items(such as Elemental Gems and PokéBlock berries).