Only thing I'd be concerned with the Tesla is repair accessibility in the event of an accident. I think those long waits were mostly early on, as Tesla was seriously struggling to keep up with demand for production. Their facilities have been expanding a lot just to try keeping up still. You're on a long waiting list if you order a new one. But I'm not too worried about it. Longevity of itself, there is no concern. The long term life of the battery packs are pretty dang proven at this point by people running up the mileage.
I think I read that an EV only has around 11k parts, compared to around 30k (per Toyota supposedly), so at least diagnostics should be much more straightforward.
But price wise of it currently, I just can't justify it other than "because I can afford it." That's not good enough. Perhaps after I get my money's worth with the rebuilt expedition in 6 years or so, some awesome new EV pick ups or SUVs will be around at a price I'd be willing to do? Or keep the expy around and get an EV sedan?
The Fusion is fine for now, but it does have some minor issues that I cover up with routine care for it. Also getting high up in mileage.
The fusion was purchased as a second car years ago, but it no longer has that purpose. It's been kept around as a back up, like you're suggesting, for while I was working on the Expedition, but it's now time to let a good mechanic tackle it rather than this weekend warrior (plus, CoA would have a fit if I did an engine swap here lol). But the insurance just isn't worth it on two low values vehicles. I live close to work now...an Uber or Lyft for a week (or just a basic car rental) isn't going to break the bank, if I own just 1 vehicle. Actually had to uber for a few days while I waited for a new fuel pump to arrive. So that's the other thing--the Fusion isn't that much younger. All those 10 year replacement parts are about to be coming up. Already put in a few new sensors.
The $7k+ price tag is much more than just the motor. Around $2k in labor (cash discount). The remanufactured engine with a 5 year no fault warranty is around $3.8k. The rest of the estimate is new catalytic converters, new exhaust manifold, power steering pump, water pump, radiator, new fuel line, and such things. When that big engine is up and out of the way, the labor cost for other parts to be replaced is much cheaper. 
I can handle most car care repairs & such myself, so vehicle upkeep is cheaper for me than others who need to see a mechanic to get a cvt sensor replaced. I've also become very familiar with the parts of this expedition over the years. lol
The reason to not go with a used motor is similar to why I'm opting to repair this Expedition over grabbing a newer used. Up until 2015, the same engine was used. With all the same design flaws from the early 2000s. The remanufactured engines get rebuilt to eliminate those problems.
I like to have something that can tow plenty, as well as a high payload capacity. A pickup would fit this, but I prefer the full size suv for trips into the mountains with friends. During winters, the Expy has proven to be quite the utility vehicle.
Among full size suvs, the expedition best fits my purposes. Most are kinda small & lacking in tow/payload like the Armada, too. Only the suburban is a real option, but certain things I don't like about it (such as no independent rear suspension, yet manages to tow less--what?!).
Anyway, in 2015 came the twin turbo v-6s for the expedition. Thanks to the 2018 redesign, the 2015-2017s can be had at a great price. Around 30k. Which is tempting. But...it wasn't until 2017 that Ford learned what companies like Toyota and BMW had about long ago in regards to fuel injection with a turbo'd engine and carbon build up...so yea, don't buy an EcoBoost engine until 2017, folks! (And if anyone already has a pre-2017 EcoBoost, it is recommended that you slam down on the throttle for a moment every once in a while).
SUVs that aren't the expedition or suburban mostly fall into the cuv category, minus maybe the 4runner. Those cuvs have the same workings as a sedan, so I'd rather take the fusion over a 15k crossover. It's pretty solid in winter weather and has a good ground clearance. But it's not climbing the side of a steep mountain during a blizzard while transporting the crew, like the expedition has. Had a fully loaded trailer in tow during a storm and had to back it up hill on a crazy loose-rock driveway that had near 2 feet of untouched snow on it. Was crazy. The trailer wheels weren't even rolling. It was just the Expy pushing it up the hill, in reverse. A cop even stopped to watch. lol
But yea, hard to justify a 30k loan even at top rates, if you have the option to fix up a good vehicle. You should find yourself in a good spot with your 8k repairs. Even if your car explodes 2 years after...you then only paid about $333/month over those two years. Cheaper than most car payments.
If I were already in the market to buy a 40-50k vehicle, then the Tesla gets to be in the conversation again. If I could find a nice P85D under 35k, the "because I can afford it" argument might be enough, though, haha.
I guess by being cheap, I don't have to worry about my dog's nails in the Tesla's interior.