Getting back to basics here. There are no transaction fees on Hive and the block producers get compensated by inflation, if token holders vote for them as witnesses. Why does the second layer have to have transaction fees as a model for compensating block producers?
That's definitely a good question!
There are transaction fees on Hive, they just work differently than most of other blockchains. You could definitely pay block producers (BP) with inflation on the second layer too. But, then you have to find a utility for these tokens otherwise your BPs are "working" for free (or for tokens that are worth nothing). Also, having such tokens will definitely trigger speculation, which I would really like to avoid. Let's say a transaction costs $0.00001, then no matter how the price of Hive goes, you'll still pay $0.00001 for your transactions. I'm not saying that the users have to pay for everything, developers can pay for the fees (or part of them). When you host your app on AWS, you have to pay for the usage, same goes for blockchains. Also, when you let people run arbitrary code on your platform, you want to have a way to limit them, otherwise they'll start eat up all the ressources available.
Yep, so the concept of Resource Credits was born to quantify and put limits on resource usage. It sounds like you are dealing with all the same problems of the base layer. And these problems were solved well on the base layer (Hive), or at least it seems like that to me, but I don't know if you see it the same way.
Delegating Resource Credits also seems another quite useful feature that's coming which I imagine could be useful also to the second layer if it utilizes something like RCs.
Regarding utility, don't you have that problem anyways? If you pay BPs with crypto, whether directly or through inflation, the token you pay them with has to be worth something.
Regarding speculation - if the price of Hive goes up, does the cost of transactions go up? I am not sure. Maybe you have more insight. The cost of transactions is quantified by Resource Credits and it stays the same regardless of Hive price. But you accumulate RCs if you stake Hive, so there is an indirect connection between Hive price and RCs/transactions. But we've seen Hive (well, Steem) prices of $6-$7 and it didn't create any problems with transactions becoming expensive. Maybe for newcomers who have to stake it is more expensive, but it is a one-time expense to stake the tokens and then your RCs get continuously replenished. So that's a fundamental difference between the RCs model and models where you pay for transactions with a token that can be speculated on.
I need to think if there is a way to leverage the Hive RCs (or Hive Power), and maybe couple this with a "stable" token. Let's say you have 1,000 Hive Power and today the price of Hive is $1, then you have 1,000 credits available on the side chain. With 1,000 credits, you can probably trigger a bunch of smart contracts that will use up your credits at 1 credit equals $1. Tomorrow, the Hive price goes down to $0.5, that only gives you 500 credits to use up on the sidechain, but your credits are still worth $1 on the sidechain (so you're not paying less or more to interact with the sidechain, you just have less ressources available). At this point, there are no bad ideas I think...
Sounds very exciting!