What I am against is traditional skillshot heals - unless they are instant or near instant, but in that case they're more like a point-and-click AoE than a true skillshot.
We don't have any traditional skilllshot heals to really compare do we? Riot's never really experimented with it to test if they're fun or not.
And issue about ally skillshots wouldn't people trying to dodge them. It'd be people doing that on accident. Not "see skillshot - dodge". For example, say that you want to heal your low HP Ezreal who has a DoT on and your only heal is a skillshot. You cast it exactly the same moment he blinks away and he dies.
It's their kill because they would've gotten it if you didn't have a heal or shield. Same if you weren't in range or had your skill on cd. If Ezreal had bad positioning and gotten far enough away were you couldn't heal him, that'd also be on a mistake on his part.
You bring up him being reactionary and dodging, but this is still a mistake on his part. For not recognizing his allies trying to heal him, for getting that low that the DoT killed him, etc... Allies can and will get themselves killed, a point and click shield and heal might minimize the margin of error there but doesn't mean it's the best game design choice or most fun.
Do shields and heals serve to prevent damage? Yes but they shouldn't haven't any outplay potential in themselves. That they are point and click and you basically never have to work to actually heal or shield an ally besides being out of mana or dying, cd, etc... I think is unhealthy.
With that in mind, you still haven't answered why a skillshot heal would be a good idea - and just saying "to be more skillfull" isn't a valid answer
That's actually not the main reason I want them. The main reason I want them is for more enchanter kit diversity. There's a lot of potential in enchanter's lore and idea concepts to protray their abilities in a more satisfying and intuintive fashion.
Point and click heals and shields with little differences among them (ad boost, ms speed boosts) is the most boring way of all.
If more heals and shields were like Bards or Rakan's (who are not skillshots but more intuitive) this probably wouldn't be an issue. Them being skillshots just opens up the potential for more kit diversity because skillshots come in wide variety, shapes and even ranges.
**With skillshot heals there is no skill expression on you hitting your target. They want to get hit and only way they wouldn't be is on accident - which is frustrating for everyone involved. **
Actually you bring up an idea for opponents being able to bodyblock heals which could be interesting but maybe a bit too punishing. The skillshots don't all have to interact or behave the same way.
Look at Xerath's ult as a skillshot, a healer artillery mage would be very interesting actually.
If you want an example of a healer who has to aim, look at Ana from Overwatch. Different genre (Moba vs FPS) but the concept of it is somewhat the same. A healer has to aim, on fast moving targets most of time, to be able to heal. Ana's actually one of the most fun healers in Overwatch I think and more intuitive than the rest.
So I definitely disagree with you here about targeted healers not working in game. There'd have to be some translation for LoL since a character like Ana has unlimited ammo for heals but an enchanter could just have shorter cds, mana issues, etc but it could work in theory I don't see why not.