Future of Mainframe based system

After the origin of all the integration layer technology, organisations are finding it more comfortable to extend the usage of the mainframe based system. Since mainframe is still based on quite old technology, the question arise. How long can we sustain the mainframe based solution?

For all those organisation where the core of the business functions are on Mainframe based technology, migrating to the midrange new technology is still quite expensive and complex exercise. Thus they refrain and delay as much further as they can. Integration technology has given them more hope now, as they have provided various adapters and technology integration options that you can now have a complete SOA based system using Integration Technology like TIBCO consuming the resources as mainframe.

Some question still arise:

1. How extensible will be these solutions?
2. When will they saturate considering the Resources (mainframe) technology and the more modern technology in the IT Arena?

There are probably more thinking that might be going around, need to get your opinion.