For the love of everything Fallout, please let me mount up on a Radstag and ride it around the wasteland dismembering raiders and anyone else that opposes me.
If not a radstag, a super mutant's attack dog. Or a tamed deathclaw. Or a mirelurk. Or really any of the large "animals" in the wasteland.
Not only would it fun to use them as additional firepower, it would allow me to get around faster without having to use fast travel all the time.
To me, this is more plausible than driving a car or a tank around but I wouldn't be opposed to Bethesda including a variety of vehicles either.