After all "notable" placeholders are made indexable on the Welsh Wikipedia (cywiki, cy.wikipedia.org) per T117693#3038880, and before we try on another wiki, we should tweak how we select items. Currently, according to Hoo, we just use whatever has "3+ statements, 2+ sitelinks".
One worry I have, and which I couldn't verify due to T144592#3038988, is that we're currently indexing placeholders which are largely in English (or some other fallback language). One possible solution is to only count the statements which have a property and item with a label in the current wiki's language. If an item has 50 statements, the items used by those statements have no Welsh labels at all, the statement count will be 0 and the item will not be considered "notable" enough for indexing.
This can be done in parallel with T158506.