I think it’s helpful to frame this conversation in the context of L2 business models. Unlike an L1 (which imo is always implicitly a form of currency / unit of account), an L2 is very much a business: in the aggregate, it collects revenues from gas fees paying for L2 txs, and it pays expenses of L1 gas fees to post rollups txs to the L1. The difference is profit, whether it accrues to a centralized sequencer or decentralized set of nodes does not change these basic economics.
The ARB and OP tokens have large market caps in spite of being, not because of being, useless governance tokens that are not used for gas. I would warn against casual observations of their market caps as justification that an L2s token will always be valuable merely due to speculation. In reality, there is a lot of ongoing discussion in these communities to do the opposite of what this forum is proposing and start using ARB and OP tokens to pay for gas on their respective L2s.
This would become less important though if ARB and OP tokens would more directly benefit from the L2 activity. For instance, imagine a situation in which ARB token stakers earned revenue distributions of the ETH earned as gas fees on the L2. I would argue that most, if not virtually all, of ARB’s and OP’s current market caps are purely speculation that at some point these revenue distributions will be enabled (much like Uniswap).
Implementation difficulties and nuances of Bitcoin script limitations aside for a moment, the analogy in a BTC<>STX situation would be BTC being used to pay gas fees on the L2, and STX ‘stakers’ earning distributions of that BTC.
Due to the relatively unique mechanisms of PoX, Stacks already approximates these economics from a stackers PoV.
Assuming a competitive mining environment where the aggregate mining profit margin approaches 0%, then miners are paying that same amount in BTC as they are earning from STX gas fees and coinbase reward net of their cost to submit their bids on the L1. (Note the similarity to distributing ARB or OP sequencer profits (revenue L2 gas fees, expenses L1 gas fees) to ARB/OP stakers.)
Thus, to stackers, competitive PoX very closely approximates allowing BTC to used as the gas asset and distributing this asset to stackers in exchange for i) the L2 activity fees and ii) compensating them for inflation (the block reward).
Assuming a competitive mining environment and that using sBTC as the gas fee instead of STX does not change the actual gas cost per a given tx (I don’t see any discussion above about how gas is actually priced in either scenario), this overall relationship does not change by using sBTC instead of STX.
That being said, there are some potential concerns and crucial assumptions we made above:
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This relies on mining remaining competitive. In the long run, if Stacks expects a majority of Bitcoin miners to eventually become STX miners, the competitiveness of STX’s mining environment could become threatened, resulting in reduced PoX yield, and thus no longer closely approximating the above case. Currently, STX retains some utility value as a gas asset even if PoX yields fall, whereas it would solely rely on competitive mining and PoX yield if no longer the gas asset.
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There is undoubtedly net buying pressure and ‘supply absorption’ of people acquiring STX to use it as a gas asset above and beyond their immediate needs for it as gas. We can even look at on-chain data and roughly quantify the degree of impact by looking at the amounts of unstacked STX held in wallets that have made at least 1 gas-incurring tx other than transferring STX, such as using a dApp (the idea is to separate out stacked STX and STX bought purely for price speculation reasons, not for ‘leftover gas’ reasons).
Removing the gas asset utility from STX also removes this buying pressure and supply absorption. Thus, to be an expected net benefit, we would have to expect that using sBTC instead would result in a sufficient increase in on-chain activity that, assuming a constant stacking yield (which acts as a multiplier effect), there is a greater net buying pressure and/or supply absorption. This is not just some short-term price speculation matter, it is a long-term security matter, since sBTC is economically secured by the stacked STX.
Whether sBTC gas or STX gas, STX’s long-term success depends on:
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Organic recurring activity on the Stacks chain (since total gas fees is a function of cost per tx * number of txs)
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How the gas or cost per tx market functions (since total gas fees is the only net/real yield portion paid via PoX, the coinbase reward is just compensation for inflation/dilution and thus is a nominal yield but not real a yield in economic terms - see ‘real interest rates’ for anyone confused by this)
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Mining staying competitive and aggregate mining profit margins remaining low (since PoX mining is the mechanism that overcomes Bitcoin script limitations to approximate L2 revenue distributions and less competition means a less efficient approximation)
It’s not clear to me that sufficient work has yet been done to truly assess the risks, benefits, and how gas pricing would work in an sBTC fee world. While sBTC as a gas asset can be economically sound, this is not a decision I would rush into or say has minimal concerns.