Even with all that work don't you think this thing should be added since privacy is involved here?
I think it's good to keep this optional. I have Bitcoin addresses that I used 10 years ago, and I could easily check their balance in case one of them receives a transaction. If those would be Silent addresses, I'd have to rescan 10 years of blockchain just to see if any of them received anything. If you sync an old wallet on Feather Wallet (Monero), that gives you an idea of how long that's going to take.
Or does it comes with other disadvantages? More cost? Please enlightened me if you can. I really don't know / can't understand why this isn't suppprted by many.
For one, I'd expect the light wallet's server load to increase significantly, and I expect it's implementation to be more complicated. But I don't know all the details.
I do know I wouldn't want (nor need) to use this for all my transactions.