Taxis don't queue at Makkasan.

Don't think anybody suggested they did, they queue at the airport though, and that's where I would get one in the OP's scenario.

Cost about the same as all the other transit too, no?

Take airport link to end of line:PayaThai (first hurdle is getting luggage down about 20 steps to get to BTS). Take BTS 'Bearing Line' to Asok BTS. To get to Soi 20 walk across sky walk to Exchange Building use escalators to get down to Sukhumvit road level and walk to Soi 20. If your luggage has good wheels it could be ok, Soi 20 is a 5 to 10 minute walk, the rest depends how far down Soi 20 you are going. Xx I think the train/BTS option is great but it does depend on how you can manage the luggage xx

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Take airport link to end of line:PayaThai (first hurdle is getting luggage down about 20 steps to get to BTS). Take BTS 'Bearing Line' to Asok BTS. To get to Soi 20 walk across sky walk to Exchange Building use escalators to get down to Sukhumvit road level and walk to Soi 20. If your luggage has good wheels it could be ok, Soi 20 is a 5 to 10 minute walk, the rest depends how far down Soi 20 you are going. Xx I think the train/BTS option is great but it does depend on how you can manage the luggage xx Sent from my iPad using Thaivisa Connect Thailand

The is an elevator that one can use to avoid the stairs.

I'm confused as to why you would suggest that someone travel to Asoke/Sukhumvit intersection on the ARL via Phaya Thai and the BTS thus involving 8 extra stations when they can just as easily take the MRT from ARL Makkasan station to Asoke which is 1 station away?

The MRT connects via 2 sets of escalators with the same BTS pedestrian link to the Exchange tower. Your suggestion involves more time and extra hassle does it not?

http://www.bts.co.th/customer/en/02-route-current.aspx

Also note that both the escalators between the street level and the mezzanine level of the BTS here become uni-directional at certain times of the day, so you may end up having to carry your bag(s) up and down at Asoke BTS.

Is it not only during the afternoon peak that those street level to BTS mezzanine level escalators become one directional - up, from 5-8pm? ie. no am peak with both escalators set to down.

I don't even recall using the stairs in the am to go up since this was introduced 8 months ago and I think the signage only pertains to the afternoon? Happy to be correct on that one loma.....