I've always said this in the past, but I don't think that MCI should be kept alive right now. The gamemode type is outdated. Its been a difference of time, mostly, in my eyes. That isn't to say one iteration is just better than another. If I'm perfectly honest, I'd say that this version would be my personal favorite. That doesn't mean that I think its the best, I think best is a VERY subjective terms. We can look at different factors for each gamemode that made them stand out, be it in their control or out of it.
Gameplay
I stand by the belief that this is the most balanced iteration of MCI, followed by 1.0, then lastly 2.0. The balance of each of these is different. In 1.0, it was really hard for Humans until they prestiged. In 2.0, it was hard for Infected until they leveled up a bit. In 3.0, both scale at a relatively same pace (minus a couple of perks being useless and a couple of kits being useless). I find the most difficulty surviving in 1.0, but that brings up another factor, skill of other players.
Skill Level
As time progressed, people got better at Minecraft and more resources have become available to become better at PvP. People didn't even know that jumping in the air makes you take more KB back then. With that, balancing has to change a lot to compensate so the game is more fair for all skill levels. This is a personal take, but if this version of MCI was released back when 1.0 was released, I would say it would thrive equally well if not better. This segways into my next topic, another factor thats out of the server's control, Youtube.
Youtube
Think about Youtubers back in the day like Jerome and BajanCanadian, they willingly played MCI and played it because they had fun with it. Now, we would have to reach out to them and have them get on to record for us at a price. Not to mention, they viewers they got per Subscribers has SIGNIFICANTLY decreased. This is also semi true for 2.0, but not in the sense that they willingly came on. By the time this MCI has come out, most Youtubers don't do long progression gamemodes like this unless EVERYONE else was doing it (example, Skyblock). No one plays Mega Walls on Hypixel because its surrounded by hackers and isn't appealing (an hour long gamemode as well as something that has high progression standards). The climate of videos has changed from committed gamemode videos to short, bursts of content where its one and done on niche gamemodes. Not to mention, this game isn't on Hypixel. Even back on 1.0 and 2.0 days, people would leave to just play Hypixel because they have so many different things on there. I've talked to people way back in the past when I met them on Hypixel and they have gone on record to say that since they don't get global progression on Hypixel, they feel like its a waste of time for them. They know MCI won't last for too long and would rather invest time into a server that has no foreseeable end.
Community
I think its safe to say a lot of us are older and busier now. A lot of the people who joined in 1.0 and 2.0 have grownup in the past 6-8 years. I started playing MCI when I was just barely 12 and I'm almost 20 in three months. I still like the gamemode, but I have other priorities and I don't want to play right now because when I do play something, I want to play with more people and have more fun, and I don't have fun right now with less people. Its a perpetual issue where no one joins because no ones on, and people leave because others are leaving. This happened on 1.0 and 2.0, too. If we want to get anyone in our community, we need new, younger players, but most interests have changed significantly for younger audiences. Kids have better PCs now, they play different games that, I personally, could only dream of playing back then. I had a dell laptop and played MCI only because I could play MCI. I didn't have a Playstation or Xbox to play COD, I couldn't play Halo or anything, I had MCI, and I enjoyed it, too. But now, kids have more options, especially when the standard PC or laptop is only going up.
Concluding Remarks
I don't think any iteration of the gamemode is bad. If I had to rank them on how well they were made, I'd say the order goes 3.0, 1.0, 2.0. If I had to rank them on how much fun I had, 2.0, 3.0, 1.0. I'm biased because this community is a big part of me and has shaped me, but I honestly think this version of MCI has the most potential and the best balance, but its impossible for it to thrive now. My opinion hasn't changed since last year.