$4.99 is pretty steep. Joining just two channels will cost about the same as a Spotify, Apple Music or Netflix subscription - more in the latter case. If they introduced a $10 unlimited membership of as many channels as you want, or maybe up to 5 channels or something, that would be interesting.
This is a thing that has been done on Twitch for several years now. The 4.99 isn't really a subscription, it is a recurring donation. You might get some things like special emoji or a symbol next to your name but that is it. The purpose is not to be able to view the content, it is to directly support the streamer/YouTuber.
When I was on Twitch streaming the ad revenue just wasn't worth it as most of our people were running ad blockers anyway. We also didn't like showing ads. So we just didn't make money as I really wasn't trying to make a living on it anyway. But some of my friends from that community had a lot of subs and I am sure if I put it on we would have had a bunch as we had some dedicated fans. I just didn't like pandering. Unfortunately this is going to become a thing on YT now, but it is nice to provide support other than ads.
I still feel like it's a high amount when it's the only option. I'd happily pay £10/month to split between the channels I'm subscribed to, or £2/month to a few good channels. I don't feel like I get any more value out of YouTube compared to e.g Netflix or Spotify, so I don't want to spend more than I spend on those, but I do feel like it's worth contributing some money towards the creators.
I guess your point stands about it being a donation, more for dedicated fans that want to support their favourite creators. But I feel like there are plenty of people with similar opinions to mine and the parent poster - I'd happily pay a similar price to a Netflix/Spotify subscription to YouTube, if the money was going towards creators of good content. But I'm not as interested in giving £5/month to specific channels.
Of course, almost all decent creators have Patreons these days, so I should probably go and put my money where my mouth is...
This isn't really a "cost" thing. These are essentially an implementation of the recurring-donation/"patronage" model, like Patreon. With most of the existing Patreon-supported YouTube channels, there aren't really any donor incentives to speak of. People are just giving the creator money because they like them and want them to keep making videos.
I feel like YouTube is trying too hard to protect their brand here by forcing people into a cookie cutter subscription model, rather than letting them accept support on the creators own terms.
Probably, a discounted tier for Youtube Premium subscribers. Honestly, I don't think this channel sub feature will get much traction, depends on what a channel can offer. Channels have the onus of being creative with this feature.
This isn't a subscription really it is a a recurring donation. And yes I am certain it will take off because a lot of creators now are unable to do what they'd like due to advertising sensitivity. A single subscriber brings you the money of 50k+ views. Even if 0.1% of the million + subs channels subscribed the creators would make a lot of money and be less dependent on the whim of YT demonetization.