If we're to put into account a few things that we do know about the Final Smash meters, as well as Final Smashes being used through this, I would have to say that so far, the meter shows viability as a part of the core competitive experience of Smash.
I'm of the opinion that this would be beneficial to the game and would bring in more benefits than disadvantages. Sure, you all know that Final Smashes are very powerful (but never mention that it's easy to dodge most of them), but this is actually a good thing for the speed of the game. Whether or not you would like to hear this, I think that the game would be much faster if we had them on, simply due to the threat of their presence, and the fact that using them will finish a stock efficiently.
Now I understand that the game could devolve into getting one solid interaction into the Final Smash. However, I think that the interaction would happen much later than people think it will. Firstly, how long it would take for it to devolve is purely up to how fast the meter charges itself, and it already looks like it will be a very slow charge for all players. This could, in theory, make it to where matches could go without using any Final Smash at all, due to how fast the game already is.
Secondly, most of the Final Smashes are much weaker with the meters on, which means that interactions not only have to be methodical, like other fighting games, but they have to happen later on in the game for them to work out properly. With the strength reduction of most Final Smashes, I believe that they will KO around the range of Cloud's Finishing Touch, so around 50% to 70% damage, give or take. Some will be much weaker, some will be much stronger, but they all have their own setbacks or advantages to make up for that.
If we were to take into consideration one more element for these, it's definitely the extra--and very crucial--layer of critical thinking that will happen to both players within the match. Going back to the fear of their presence, I think having the meters on will promote a faster and much more offense-oriented playstyle to both players rather than a campy and defensive playstyle. You may have people who will try to be defensive, but the mere threat and existence of a Final Smash that can and will take your stock is more than enough to convince players to try and finish off their opponent and end the match quickly enough so that the opponent has no chance of using it. This extra layer of critical thinking is what could make matches much more exciting for the players and the viewers alike. This would definitely draw in and keep viewers much more entertained than simply having a dried out system that we've all been using for nearly two decades.
Finally, while at first this will be an unwelcome change that will be tested, I believe that Final Smash meters will be the future of Ultimate and will distinguish the game from its predecessors. Even if we have to increase the amount of stocks to adjust for this, I believe the game will be much better with it on than off.
That being said, however, I also believe that we should test these out up to the first or second major tournament of Ultimate just to get a good grasp of what players, spectators and the community would think about these. Give it 2 to 3 months, then come up with the verdict. I understand that change can be difficult to grasp in this community, but Super Smash Bros. Ultimate is not like the rest of the games in the series and should be treated as its own entity when it comes to the ruleset and its philosophy.
The meters could be a welcome change in the future.