okay, so let me try explain a little bit why this is very likely not going to happen.

1. it's a "public" transportation service that's pay per use, first come first serve, there are different fee depending on time/distance/etc.
2. in order to "restrict access" say, use the commercial/residential parking lot as example, you carve out certain part of the capacity that only BC resident can use and BC tax payer have to foot the bill. The parking lot example, commercial side and residential side strata foot the bill for the maintenance and design which area/zone etc for the residential one and it's gates/etc.
3. practically, 80% of BC don't even use that service, source: https://www2.gov.bc.ca/assets/gov/data/statistics/people-population-community/population/pop_subprovincial_population_highlights.pdf 2021 about 5.2m in BC http://viea.ca/wp-content/uploads/2021/10/2021SOTI-Report-WEB.pdf 2021 report says +1.2% population for 10,272, so 100% of population is around 856k. which compare to 5.2m is 16% So I lump in another 4% that are not counted to Vancouver Island region but closely tied to the region which should be pretty fair estimate.

That means, if the people that won't use the service has to pay and reserve for the people that do use the service that would be unfair thus usually, a "toll" would be put in place to cover the cost of transportation deficit. You might ask, what deficit? To have reserved space for resident to use ferry, they have risk of running the ferries with empty space reserved for resident use. Those would have to be "over reserved" for service guarantee. If they under reserve, then you simply have 2 choice, either queue with tourist or queue for the next for resident.

4. we have not even talk about the environment impact of reserving those spots just for residents instead of doing as much full ferry each time. That cost is footed by the whole BC as a province. (assuming we do have a carbon budget)

In the end, it's all about running cost and tourism scheduling. Let me run a very simple situation. Say, a tourist group booked a trip to run a bus with everything scheduled properly. Now, if resident have priority queue, means the whole tourist bus's schedule is NOT guaranteed. If the fluctuation of local traffic suddenly spike, the tourist group might face 2 hours+ delay. Which is simply not acceptable for a tourism company to run such risk, the tourism industry might simply opt for other first come first serve transportation service. Which would have a big impact to Vancouver Island. And if you remove tourism traffic from ferry, then you foot more cost per trip or face reduced scheduling.

The fact that for all 17+ years I lived in BC I only take the ferry round trip 3 times, and yet the tax is budgeted for subsidize it for more affordable traveling for the Van Island residents I think first come first serve is a fair compromise. Cause the people the visit Vancouver Island for tourism will most likely also visit other part of province, lower cost of transportation benefits everyone.