The problem with adopting the jungle item "enchant" system for sightstones is that it would probably copy the problems of the system as well. The jungle is currently being dominated by cinderhulk junglers, with cinderhulk being so strong it's showing up in top lane. When cinderhulk was juggernaut, the warrior enchant was dominating the jungle, with vi and lee sin being a step ahead of the other junglers at all stages of the game. Devourer is okay on some junglers, but clearly suboptimal, and poachers seems to only work on Nunu.
Right now the support meta picks are determined by who can bring the most utility for the adc. If the sightstone system is changed to an enchant system, it could artificially shift the meta in the same way the jungle items have. Probably one enchant would be completely useless, except maybe on one champ. One enchant would be mediocre. One enchant would be decent, and the last enchant would be the meta enchant that everyone feels is the strongest. Champs who use the strongest enchant well would become significantly stronger while champs who don't would become weaker.
For example, two of your new proposed sightstones have mana regen (one with mana, one with ap). This means that mage supports like morgana and annie start building their ap items sooner (assuming no changes to upgraded sightstone costs, gp10 item costs, and a small combine cost, like the jungle items) and they get to have an extra ap item (cough mejais cough). Sure, leona and thresh get to build another tank item, but mage supports would be able to snowball their leads without having to sacrifice warding by opting for the "no sightstone, upgraded yellow trinket" route. We might see zyra and even brand or ryze come to bot lane, until riot decides they need to make adjustments and buffs the health enchant, resulting in a tank support meta where mage supports are practically useless, or at least starting from behind.