If the proposed Trolleybus scheme in Leeds is succesful, I think more cities will seriously consider Trolleybuses.
You would certainly hope so. There will always be some reluctance in embracing something which is seen as being an 'alien' concept, or perhaps in this case something which is still thought of as old fashioned. But the reality is that a trolley system can do what a tramway can do, with substantially lower costs.
In fairness, most places don't actually need a tram system, what they need is simply a fast, efficient, fixed link transport connection. Trams have tended to be the obvious answer simply because an ordinary bus just isn't considered 'special' enough, and a tramway has a certain prestige on offer. There is also the agrument that a diesel bus isn't 'green' enough to project the modern image most places now crave. A trolleybus system will offer that clean, fast, fixed-link solution. Now that we have bendybuses and concepts like First's 'FTR' vehicles, it's possible to engineer a trolleybus which is essentially everything a tram would be without the rails. In most circumstances, it would undoubtably be a cheaper, better solution.