I have a hypothetical.
I've done some googling and can't really find much.
Is there a reason one couldn't pole-mount a 210, kind of like a pole-mounted PA speaker?
View attachment 3918235
Like this but with a proper bass cab?
I have an 810, but it'd be nice to get my sound up near my ears
No reason you can't do this, but it won't sound much like an 810 if that is your goal.
Putting the cab at ear level will get your ears in the dispersion pattern for all frequencies, the drivers produce. With an 810, the higher frequencies still shoot by below ear level, and you get a lot of cancellation and lobing off axis, so you hear a modified response.
Another factor is boundary effect. You get cancellation at the frequency where 1/4 wavelength equals the distance from the cab to the floor. This is essentially notch is the frequency response. I normally elevate my bass cabs anywhere from about 18" to waist level.
I don't think boundary effect is really relevant if you will be standing right next to the speaker. One of my early rigs was a biamped SVT with a Fender Twin loaded with JBL E120s stacked on top for the high range. This put the JBLs at ear level and the effect was sort of like wearing headphones when I stood close to the rig.
I suggest inspecting the inside of the cab to see if there are any internal components you need to work around. Also consider vertical VS horizontal alignment of the drivers. Vertical alignment will be better for horizontal dispersion but if the goal is to stand right on top of the cab and monitor at a really low level, horizontal alignment may be better...run some experiments.
If space is available I suggest using one of the built in cups that looks like this.
A cup mount should allow your cab to function normally when it is not place on a pole and there is no hassle with removing and replacing the mount. This type of bracket does slightly decrease the internal volume of the cab, but I don't think it's enough to worry about.
An external pole mount bracket like this tends to get in the way, so you may need to remove and replace various reason. You may also have to deal with air venting through the holes if you operate without the bracket in place
Make sure the diameter of the pole mount is the right size for your speaker stands, and make sure your speaker stands can support the weight.
Also as others have suggest be mindful of where the mount is placed on the cab. I believe the mount should be placed so the cab has a slight tendency to tip forward on the mount.
Remember the drivers are in the front of the cab, so typically the front is naturally much heavier than the back. Do a balance test to find the correct placement of the adapter instead of trying to eyeball it.