That assumes the trams were a good idea
When you have landing planes practically touching the railway line, it seems madness not to have a station nearby, served by some form of light rail (whether that be a tram, monorail or something DLR-esque).
I know there was uproar when the trams were stopping at Haymarket, which meant changing from plane-tram-train to get to the centre of Edinburgh, but correctly implemented as part of the airport infrastructure, a shuttle to a national rail station would be seen as not much different to the North/South transfer at Gatwick.
A monorail to Gilmour St would be too long, I think - as with Edinburgh, it would need to be a short enough trip to seem like part of the airport experience. Move St James station (or build a new one) to just before the A737 bridge and you're within a mile of the terminal building.
Is the Paisley Corridor at capacity? Could the 4tph along the Inverclyde line be doubled as far as St James, which could gain terminating platforms in its move?
(All just back of an envelope thoughts, which are no doubt full of holes!)