I'm with Iride 100% - have said it before and will say it again - If you purposefully foister a one person horse, you are doing a huge disservice.
No one can guarantee that they will always own a horse or always be the one to handle it. Sickness, family illness/death, your own death, travel, relationships, etc. - There are a million reasons why someone eventually will need to be able to safely handle your horse.
All my horses can be handled by up to about 5 different people within a few weeks of me having them. In a few months, just about anyone could go catch them, groom them, pick up feet, check them over, etc.
Yet I still have a good bond with them.
I am also big on letting other people ride them - As long as it is done right, it fosters a tolerant horse - Which is one of the best traits you can give a horse. My little Arab, Wildey, has been ridden by probably 50+ people in the 9+ years I have had him. Begginers, experienced riders, in between, at competitions, at home, on the trail, at PC. We did squad for four years where he was ridden by 15 riders a day for two days a month. And yet he still gave that bit extra for me - There was things he did OK for others but excellent for me. It doesn't get in the way of a 'bond'.
At a show a week or two ago I had a younger friend there whos horse was put down not long ago. So I chucked her up on bundy to do some classes - And lo and behold she won a champion ribbon. I want all my horses to be like that - He was highly tuned, responsive and quick for me, and then just crusied around with the new rider without losing a beat.
It means that if I ever need to sell, I can guarantee that they will find a great home. I have always had people interested in my horses, for that exact reason. While they perform their best for me, they will get out and try for anyone.