The trouble with most radical theories of Stonehenge, like this one, is the assumption that the ultimate configuration of the monument - with a complete sarsen circle, but before half of it disappeared - is what the original builders had in mind. As if the Saxon builders of a church said to each other, "in 1200 years time, just our tower will be left - but it'll be the perfect counterpoint to the 1984 loos and the pink chairs the vicar will replace the Victorian pews with." No. Stonehenge was a living building - knocked around, no doubt with people declaring it didn't have bluestones when they were a child, for a hundred generations.
The other trouble with most radical theories of Stonehenge, like this one, is that there's no evidence. That the Pope used to be carried around is not a proof. Sky platforms on which sky worshippers could conduct ceremonies would require infrastructure to support them that simply hasn't left any evidence of existence.
Maybe the whole theory is wrong. Maybe they used the flat tops of the trilithons to expose the dead, collecting up the bones as they fell. We can all play this game.
The latest serious theories see Stonehenge, connected by the Avenue and the Avon to the wooden Durrington Walls, as the place of the dead. Durrington, with its midwinter hog roasts, was the place of the living. So looking up could be totally the wrong direction - the south-western horizon is where to look. The place where, bringing warmth and light to the dead - clustered in barrows around the landscape - the sun comes itself to die.