The previous posters are right. The Scheduled market from GLO will always be limited by the competition from BRS & BHX, but that doesn't rule it out completely. The Channel Islands are a dead cert, all year round and there'd probably be enough of a 'niche' business travel demand for a Paris/Brussels/Edinburgh. If you could get into London City or Heathrow cost effectively, then you'd be able to compete sensibly with the rail service, which is still slow (2hr 15) and relatively expensive (£60 single).
The real benefits for GLO will be in the corporate market. The business is already there, but currently being lost due to the operational restrictions of a short runway and non-precision approach. This is; however, a difficult market to stimulate so the Airport will always be reliant on it's existing strong GA and Commercial training, which will be boosted by the installation of ILS