1) Bitcoin XT
Allows the block size to increase exponentially to the point, where home-based nodes will no longer be able to participate in consensus.
I don't agree with that assessment, for four reasons:
1) Technology continues to improve. e.g. $100 worth of hard drive space 15 years ago costs about 17 cents today.
2) Block size cap != block size. The cap is 1MB now, yet we have no 1MB caps. The blocks will increase as needed to store the transactions that we have. Assumptions of 100% filled blocks are baseless.
3) If the increase based on transactions is still judged too quick, the miners can always choose to include only some of the transactions, based on size, priority, fee, their mood of the day, etc.
I invite you to re-assess the parameters of the system (including the block size cap) not only based on technological considerations, but from the perspective of incentives structure as well. The fact, that we haven't seen enough consolidation in the space of full nodes, is because the rules of the game clearly indicate that there is a ceiling on the level of bandwidth that the network is willing to tolerate with its current size. Don't sign up to the rules, that you likely won't be able to follow in the future.
4) BIP 101 is not the end-all be-all. It's a best-guess shot in the dark. If it needs to be adjusted, it can be. It can even be adjusted down with a soft fork.
Hearn and Gavin made a mistake by releasing XT with BIP 101 with a 75% activation rule. They made a further mistake by including unrelated changes in XT. We should not let these issues confuse the examination of the block cap increase BIP alternatives. The simplest of the alternatives that actually has a chance to meet demand is BIP 101.
Why shoot in the dark? It's like trying to solve the problems of 2020 or 2036 today, without even knowing what they are. Don't underestimate the psychological effect of the limit. That's the only reason we are having this conversation about the change. It's a sync-point (or barrier in pthread terminology) at which we all arrive to see who is running and where we are going. Without these the inertia of the process might build up to the point, that any attempts to hold it within the path, that best represents the goal it was created for, simply won't gain any momentum and instead fall on deaf ears.
There must be a single static limit firmly cemented into our perception of Bitcoin in order for it to have any effect whatsoever, but big enough not to limit Bitcoin's growth within the safety threshold determined by the current state of technology.