I would like to suggest a somewhat different approach to this than the binary “Polkadot Treasury pays” vs. “each parachain pays” model for services (not just Subscan) where there is likely some common cost for the provider and then a decreasing marginal cost for each additional parachain. I suggest that this forms part of the future of the Parachain Technical Fellowship (PTF) and the future of the Treasury.
The PTF would be another instance of the Ranked Collective pallet in Polkadot’s Collectives parachain. Gav mentioned this idea at Sub0 last year. Rather than the existing Technical Fellowship, which is focused on assembling a group of experts in the Polkadot protocol, the Parachain Technical Fellowship would assemble experts in parachain development and operation. Like other collectives, when coupled with an instance of the Referenda pallet, the PTF could control a number of pre-defined origins.
One (or several) of those origins could control an account (on multiple chains) corresponding to another instance of the Treasury pallet (the logic of which would sit alongside the PTF). Of course, by default most or all new DOT would enter the “main” Treasury, but collectives could have their own treasuries too. The PTF could make one (probably quite substantial) proposal to the main Polkadot Treasury to fund the PTF Treasury. Then, the PTF Treasury’s SpendOrigin would correspond to some rank-weighted quorum/approval of the PTF, and could decide to fund initiatives that benefit all parachains somewhat equally or address common pain points for parachain developers.
There are many more applications of this pattern. For example, the Ambassador Program could also have an instance of the Treasury pallet, and request a yearly budget from the main Treasury for things like events. Then, high ranking Ambassadors can approve event spending, instead of coming to the main Treasury every time someone wants to host a meetup.
For many collectives, I imagine they will manifest as a bundle of Ranked Collective, Referenda, and Treasury pallets. Each collective’s origin can control its own Treasury, make spending proposals to the main Treasury, and perhaps have certain other governing privileges (e.g. Technical Fellowship having WhitelistOrigin, and PTF having an origin that can unbrick parachains).
Using this model, the PTF could fund infrastructure that is common to all parachains, and decide how to allocate its Treasury, while still leaving individual parachains the freedom to supplement that if they want specific additional services or something custom.