I would love a Frontierland station, but not if it meant getting rid of the Toontown station. The Toowntown station's awesome for families in that section of the park, that are leaving for the day and don't want to have to drag their cranky, tired kids across the park.
You are proposing a switch, but you could not feasibly switch Fronierland and Tomorrowland. The only conceivable place to put a Fronierland station would be at the location of the Jamboree. Not that it isn't a good place, but it's true that like 100 feet down on the other side of that tunnel is the Toontown station. The trains wouldn't be able to run like that. Eliminating the Tomorrowland stop would force people to stay on the train and go halfway around the park, with no stop having good access to Tomorrowland, including the Monorail and Matterhorn. Not to mention any removal or replacement of Toontown station means a much much longer walk for anyone in most of Fantasyland or all of Toontown.
I understand that you are thinking of thematic reasons, but there is a reason there are 4 stations and why they are spaced fairly evenly. It's to allow the trains to operate properly. When previously there were only two trains and two stations spaced closed together, you got on at one station and were forced to ride the grand circle tour with no stops along the line. I think people would prefer being able to get off where they wanted!
If you look carefully at the billboards near the entrance to the Tomorrowland Train Station, it actually does suggest some sort of time travel. :)
In short, no, there need not be a Frontierland train station... especially if there is an expansion of Frontierland as it seems there could be on the horizon.
A path a mere 300 ft long could be put in following the path of the railroad tracks back to Frontierland from Toon Town station easily. This would considerably shorten the walk to the land from this station without necessitating moving it and all the equipment that would go with it nor having to rework the rules for stopping, etc.
As to having the train stop in Tomorrowland breaking theme, it most certainly does not break theme. The station's theme matches the surrounding land in style and color. Having a train go through works as it is completely possible and believable that in the future they would have at the very least a recreation of a steam train as a museum piece of sorts for people of the future to experience.
Or you could look on it as being the boundary of the park and existing outside of the theme's of the various lands, being the vehicle that takes you on the journey to the various realms of fantasy. Either way, it fits and I see zero reason to remove the Tomorrowland station.
You also chose to ignore the idea that the train is what circles and encompasses the park passing through four very distinct lands as a sort of "journey" though the worlds of yesterday, tomorrow and fantasy.
Now, if Tomorrowland was expressly some alien world, having a train there would be a bit odd and questionable. However, as we have cars and submarines and are clearly on Earth, it isn't out of the realm of the believable for it to be there. Putting the future in the past (monorail in Frontierland) would be odd, but having the past in the future is not strange at all. The future is, after all, built upon the past. In order to be believable as the future at all there should be details of a past anyway, otherwise is just comes off as forced, contrived, cartoonish. You want layers of reality in any world.
In short, I think the train fits absolutely perfectly within the thematic bounds of Tomorrowland.
Not feasible, but I wish it stopped in every land!
a frontierland station would be great, especially if the land expands into the circle d ranch. a train station could be a highlight of sorts.
what i would do is take the toontown station out, and assuming they are planning on replacing autopia, move the tomorrowland station more in that area. i still have my fingers crossed for a discovery bay type land there, which of course a steam engine train would fit perfectly... anyways, that would keep the number of stations to 4 & keep them evenly spaced, and it would fix your issue with breaking theme in tomorrow land.
if they do expand frontierland and can't make a station there, maybe a quick show (similar to the train robbery at knott's) would be suitable.
As noted earlier, Frontierland already has a railroad station; Some older signage still references this:
If I was going to add a station, it would be at The Hungru Bear. Everywhere else in the park is already easily accessible via train or by foot.
New Orleans Square station was Frontierland station and still is, in as much as New Orleans Square is a sub-land or addition to Frontierland.
The signage, the last time I saw it, had "New Orleans Square & Frontierland Station". I think as the land is right now, a train station would put the station way too close to Mickey's Toontown. If they do expand into Circle D, then it could be possible.
Adding a station may play havoc with the efficient operation of the trains.