Mainframe technology is here to stay. Just add innovation.
Where mainframe computers are concerned, the Technology Spectator says it better than I could:
In a world where IT continues to power forward, the longevity of the mainframe and its place in today's computing environment is increasingly being questioned. With 'change' often confused with 'progress', a mainframe's durability can work against it. As demand grows for more agile and innovative systems, it is difficult to reconcile a technology in its sixth decade with the technology we carry around in our pockets or use at home. But while dissenters continue to challenge the validity of the mainframe, the technology keeps on proving its worth.Few consumers know or understand that "ancient" mainframe technology is working behind the scenes in the banking, travel, and insurance sectors, and that's unlikely to change. What is changing though is the insertion of start-up mentality and innovation into the mainframe ecosystem, like Splunk, a search specialist, teaming up with Syncsort to unlock some of the data being produced by mainframe systems. What does not change though, is the fact that mainframe systems require specialized skill sets, and those experts are getting hard to find. Not a good thing in an environment of ever-more-stringent compliance and regulatory requirements.
Mainframes can run java. No googling first? Try http://discuss.fogcreek.com/joelonsoftware2/default.asp?cmd=show&ixPost=38317 for a start.
It is like everything else in Life and IT. Everything has a place and purpose. If your need is to process millions of transactions per day the mainframe option starts looking very good. Need a web server and an app built in a hurry then Intel server bubbles to the top of the list.
Your reference to 'terminals' is quaint. You will find that few programmers have a 'terminal'. Mainframe is accessed via a 3270 emulator which is generally a program running on a PC, or more likely an app in a web browser.
Programming? These days an IDE running on the user's PC can interface with the mainframe, pull the code up locally, compile locally, and push the code to the mainframe for compile and promote. Code promotion? Package and promote code from your IDE.
The mainframe has a TCP/IP stack. What can't be built? If you have one, then you may as well use it as much as you can.