OK... but that concern seems a bit artificial.. if bigints are appropriate: use them. If the table won't get to bigint sizes: don't. I've even used smallint for some tables I knew were going to be very limited in size. But I wouldn't worry about smallint's very limited number of values for those tables that required a larger size for more records: I'd just use int or bigint for those other tables as appropriate. The reality is that, unless I'm doing something very specific where being worried about the number of bytes will matter... I just use bigint. Yes, I'm probably being wasteful, but in the cases where those several extra bytes per record are going to really add up.... I probably need bigint anyway and in cases where bigint isn't going to matter the extra bytes are relatively small in aggregate. The consistency of simply using one type itself has value.
And for those using ints as keys... you'd be surprised how many databases in the wild won't come close to consuming that many IDs or are for workloads where that sort of volume isn't even aspirational.
Now, to be fair, I'm usually in the UUID camp and am using UUIDv7 in my current designs. I think the parent article makes good points, but I'm after a different set of trade-offs where UUIDs are worth their overhead. Your mileage and use-cases may vary.