Does Rumble Scrapper equipped with Skyfall of Areion while conquering with a Blue Sentinel play 2 mech tokens?

No — still 1 Mech token. Skyfall of Areion only widens which event satisfies Rumble's "When I hold" condition; it doesn't make the trigger something Blue Sentinel can add to, and a single Conquer is a single trigger (FAQ #9733).

Blue Sentinel's passive is scoped to "your hold effects for holding here" — it modifies triggers that happen because you held at that battlefield. Conquer and Hold are separate scoring methods (Rule 469), and Skyfall doesn't convert your Conquer into a Hold (FAQ #5622: it adds legality for both events, it doesn't duplicate). So when Rumble conquers, his hold-effect-turned-conquer-effect triggers once, and Blue Sentinel adds nothing.

For contrast: if Rumble (with Skyfall) were present at that battlefield and you actually held it with Blue Sentinel there, the hold trigger would fire twice (2 tokens). Likewise, if a Reckoner's Arena-style effect explicitly activated his conquer effects, you'd get an extra token that way — that's the mechanism that produced the double trigger in FAQ #7492, not Skyfall itself.

Note: no official FAQ covers this exact Skyfall + Blue Sentinel + Conquer combination, so this is the reading driven by FAQ #9733 and Blue Sentinel's "for holding here" wording.