Glasgow would enhance the Premiership but does Glasgow need the Premiership ? Local Derby would change from Edinburgh to Belle Vue ,travelling fans (of which Glasgow have a large number) would have horrendous traveling distance with the rest of the Premier being so far south. Also not sure bigger speedway names would have major attendance increase in Scotland, higher costs with restricted income would be inevitable.
Would be entertaining to see Glasgow in the Prem and on TV but think Glasgow will continue to build its infrastructure before considering moving up IMHO