The same shape it is now ... a dome.

I would start by establishing the outer shape first, to whatever size you want, and then look at what's left that you have to work with, in order to decide what else needs to go away.

If it looks like the first photo all the way around the plant, then I'm not sure any pruning is called for. In our climate, rhodies can grow to a significant size (even the so-called dwarfs) and look best when they are just left to their own devices when space allows.....as it does in this case.

My inherited garden has a collection of rhodies dating from the early 60's when the house was built. Several are close to 20' tall and nearly twice as wide. They never get pruned. The only ones that receive any pruning attention are those included in planting beds with other shrubs and plants and get trimmed back every so often so as not to overwhelm their companions.

I should have mentioned that I do kind of have a shape in mind. More tree like, showing some leg, as Mike (BoTann in the old days) would say. My wife and I visited some gardens on lake Como in Italy and there we saw the tallest rhodies I've ever seen, easily over a hundred feet. I've also seen some tall, tree like rhodies in the Arboretum. So different from the round shapes you usually see.

I could be fine leaving it alone, but if I could remove some of the tangle, expose some of the larger inner branches without making it look like something from a Dr Seuss book...Hmm, maybe that wouldn't be so bad. :o)

Your plant doesn't have an already tree like shape that suggests arborizing it. Quite the opposite in fact, with it instead being a broad dense mound. Also the value of showing a little leg depends on those legs being nice looking, as in having attractive bark. Something that many hybrid rhododendrons don't have that much of. (Same with English hollies and numerous other kinds of evergreen trees and shrubs that get limbed up frequently, to their visual detriment).

My wife and I visited some gardens on lake Como in Italy and there we saw the tallest rhodies I've ever seen, easily over a hundred feet.

Are you talking about the tree rhododendrons at Villa Carlotta? They are truly magnificent, but I agree with the other comments that yours doesn't lend itself to having its legs exposed. It's lovely as is!

Yes, Villa Carlotta! Just amazing, like something from the land of the giants.

I believe @Embothrium may be right about this. One of the issues I am concerned about is the larger, structural limbs are rather far apart. Pruning to expose those could make it look like Picasso Poodle.

Thanks to all for your thoughts.

From Villa Carlotta web site - scroll down to Tree Rhododendrons

https://www.villacarlotta.it/en/garden/

https://www.rhododendron.org/v34n3p125.htm

https://www.finegardening.com/article/3-ways-to-prune-rhododendrons

Interesting, am I understanding correctly tree rhododendrons are a different species than the shrub rhodies common here?

Yes juniorballon, there are different varieties of rhodies. I am sure the giant ones I saw at Bodanant gardens in Wales would never survive the Texas heat that my little Encore azaleas do. I rarely prunes them because my dear hubby keeps stomping them hanging Christmas lights and gutter cleaning. Even when I put tomato cages over them he still managed to weed whack some. They are still surviving and hopefully chopping out the jungle of yaupons and Asian jasmine will let them grow.
As for those gorgeous rhododendrons of the original post, I suspect it has too many main branches or trunks to shape into a tree form. But you could look for low branches to remove to "raise" the canopy.

Yes. Rhododendron arboreum is known as the tree rhododendron, although other species can grow to significant heights. Our native species, R. macrophylla, is often found stretching up 25-30' or more. The shrub forms one finds in most gardens and nurseries/garden centers are rather complex hybrids.

Since you live in the area, I'd encourage you to visit the Rhododendron Species Foundation garden in Federal Way once restrictions are lifted and free travel resumed. Not only is it a gorgeous botanical garden in all seasons but it is the largest collection of rhododendron species anywhere.

It has been on my list to visit the Rhododendron Species Foundation garden for far too long. Would be a good way to celebrate the lifting of restrictions.

The only way you are going to get rid of that 30 plus 15 year old tangle of branches is to cut the rhodo back to the nub of the main trunks and regrow it from scratch. At 45 years old it might not respond with much enthusiasm. It looks happy enough and could regrow just fine and be back to full flower in two seasons. That hard of a prune on an old rhodo does have some risk.

Clearing out that tangle is not really necessary. It's not affecting the growth of the rhody and is not very visible, at least from the views I can see, so wonder why even contemplating any pruning. The plant will not be enhanced by having its "skirts lifted" and while you can hard prune large, mature overgrown rhodies - have done it many times - it takes longer than just two seasons for them to start putting that growth back on and looking good.

IMO, it looks just fine the way it is.

The structural tangle this shrub has doesn't lend itself to making into a tree. Why not start out somewhere else with a new young pup and take it in that direction?

I'm just going to leave it. I may look into getting a true tree rhododendron. Perhaps, long after I'm gone, someone in 50 years might get to see a 50 foot tall rhody in full bloom..