You can use jPOS underpinnings to build a switch implementation that replicates any and all of the features found in products like IST/Switch, BASE/24, ON/2, Postilion, etc, etc. The only limits are your imagination, the amount of time you have to construct your solution, and the capabilities of your team. Remember, this is software, and like most software - it can be used to construct a good solution...or a bad one. You'll want to run it as a professional project, do proper design and testing, manage the transition off of IST/Switch in a risk-averse manner, etc. None of that should surprise you.

jPOS can help you act as acquirer or issuer, can be strict one-to-one or one-to-many, can do passthrough processing or act as host. Not inherently, mind you. You and your team would need to build that capability on top of the jPOS framework, which does not inhibit you in anyway from any of those directions. The 'zing' you get from jPOS is that it eliminates most of the grunt work associated with complex ISO8583 messaging implementations and its corresponding security requirements, thus allowing you and your team to focus on more 'value added' activities. Your marketing and sales team don't know/care about your work on ISO8583...they simply care about whether you can support new card products and/or features, new devices, new points of origination. A jPOS framework allows you to reorder work to focus on customer-focused activities like that.