The only argument I have seen that kind of / sort of holds any validity is poor people in really impoverished areas can't afford to run a full node.
If they have a problem to run a node now, then all their issues will remain, no matter if BIP-110 will be activated, or not. It doesn't matter from the Initial Block Download perspective, if you have 4 MB with only payments, or 4 MB with only data pushes. Actually, if you have OP_RETURNs, then they make blocks smaller, because instead of having 4 MB witness data, you have 1 MB legacy data. And also, validating OP_RETURN is faster, than OP_CHECKSIG, and a lot of other opcodes, so it can only accelerate Initial Blockchain Download, instead of slowing it down.
The "we don't want to store other peoples data"
Bitcoin was always about processing transactions, which were made by other people. Think about it: if you have a chain, where you have only your transactions, and nothing else, then the whole history is crystal clear, easy to track, and it is obvious, who owns what, which means low privacy. The whole point of accepting other payments, is to "hide in the crowd". Blocking any transactions would just reveal identities faster, than they would be in normal circumstances, because the less transactions there are, the easier is to track a given user.
Which is why even SPV users would be a bit safer, if they would handle more data, than just related to their own payments. For example: if you have some SPV node, and it asks about your address, and absolutely nothing else, then SPV server can easily track that user. However, if you request the whole block, then you can scan it, and find your payment, without informing anyone, which address is yours.
Hopefully some miner deliberately mines a couple of blocks that are 110 incompatible so they split off sooner.
They won't split sooner, than during "mandatory signalling". Because otherwise, they would split here and now. And they still follow non-BIP-110 chain, so we have to patiently wait for the block 961632, and then, a single non-BIP-110 block will move them to a different chain. Then, they will always split, if they will be in any minority. And the speed of their chain will be proportional to the split of the hashrate. If we assume they will get 1% or 2%, then they will produce something like one or two blocks per day.
In general, if someone wants to get an idea, how fast BIP-110 chain will be, then all that is needed, is to trace their signalling blocks. Let's assume, that the blocks they mined are the only blocks they have in their chain. And then, it is a question: do you want to use a chain, which can produce one or two blocks per day, instead of one block per 10 minutes?
At a 10000% guess it was them renting hash to prepare and making sure everything works.
Which is good, because if they would reach 1% or 2%, then they will split, and use their own, slow chain. But if they would have 0%, then BIP-110 would simply fail, and we would still have to deal with them. Having a little hashrate is needed, to get rid of them. And later, when their difficulty will adjust, they will be not that much different, than altcoins, which hard-forked instead, like BCH. Because even if they will have a soft-fork, then still: a minority soft-fork is still a fork. As more and more time will pass, it will be harder and harder for them, to revert BIP-110, and unite with the original chain, or reach enough mining power, to replace it.
Would be nice if it happened sooner since these arguments are getting repetitive.
Well, many changes could happen sooner. But they still want to stick with their original timeline, to create a perception, that there is a chance to reach bigger hashrate.
Also, they still keep things, which are not needed, for example disabling BIP-110 rules, after a given time. It won't push them back to non-BIP-110 chain. Coinbase transactions will split coins anyway, even if there will be absolutely no replay protection. And there actually is: a single output, violating BIP-110 rules, is enough to split the coins. Then, Core will process and include a transaction with simple things, for example single P2PK use, and BIP-110 chain will reject it, and mark it as "not a payment" (because obviously, Satoshi using P2PK was a spammer, and not a real user).