The original tech demo had a 'long play mode' style, where you played one arena at a time, and had to get 50% to unlock the next arena. Upgrades were persistent too. Gold previously collected was only worth 1 instead of 10. Each arena got harder and harder. So the first Episode 2 Arena would be much harder than the final Episode 1 Arena.

This worked great for a single Episode, but scaling the difficulty (balance curve) was pretty difficult across multiple Episodes. We created Time Clickers to learn more about extending gameplay via a long and addictive difficulty curve, judging by the hundreds of hours people put into Time Clickers, I think we've figured it out :)

So we have a rough plan for the future that looks like this:
1. Create a free multi-player shooter building on the concept of the voxel world from the Daily Challenge level editor (This gives us 2 tools we need: multi-player & level editor)
2. Create a sequel to Time Rifters that incorporates the addictive long term progress curve of Time Clickers with the first person voxel shooter & multi-player.

It's a pretty fuzzy plan, but we want to develop in the open as much as we can, we'll release a tech demo for the next phase as soon as we can (hopefully early 2016), and make sure we get player feedback as we develop to help it evolve (that's what I think Early Access is really useful for).

We're really happy to see people enjoying Time Clickers & Rifters, it pushes us to create more cool stuff!

While I'm not necessairly suggesting that I want the progression pace to match time clickers, I just thought it worth noting that within a single "play through" of time clickers (that is, the time from starting a run to time warping), one can complete the entirety of the main game in Time Rifters, probably a few times over. The post-campaign content adds a lot of value to the game, of course, and I love the daily challenge, and making your own rooms is fun too. :D

I really like the idea of a fully multiplayer take on the game though, and I'm exicted to see what you do next! (I also think it would be a cool idea to have a syncrhonous but turn-based mode: that is, you're playing like normal except with people online, each player going in sequence cooperating with the life of the previous player).