Yannick Mahe has posted some thoughts (from personal experience) about living with a legacy framework and some of the consequences that come with it. In his case, it's a Symfony 1.0-based application that would require a complete rewrite to migrate even up to the Symfony 2.x range.
At our company, our main web app is based on Symfony 1.0, a PHP framework released in 2008. It was developed by a company called Sensio and open-sourced shortly after. It was a great framework when it came out, with all the good ideas from Ruby On Rails, CakePHP, etc. as well as great documentation, tutorials and a growing community.
[...] Since that framework came out, its subsequent versions, Symfony 1.1, 1.2, 1.3, 1.4 came out and died out. The 1.4 version came with a 3 year long term support promise from Sensio which ended in 2012. All the 1.X versions are based on the same overall architecture, and same principles. Sensio also released Symfony 2.0, 2.1, 2.2 and very recently, 2.3. which have a whole new architecture.
He talks about some reasons why they're not migrating (the risk involved, the product focus, etc) and some of the trials they did to see what kind of effort would be involved. He then puts some context around working with a legacy framework, pointing out that:
- You can no longer rely on the community and time is lost figuring things out yourself
- Documentation is harder to find
- The ecosystem (ex. plugins) is no longer seeing new features or updates
- The compatibility issues with newer versions of PHP
