If you're a partner of PTC, you should contact your partner manager who can advise about joining beta or early release programs. These sort of things need to be vetted and approved by product management.
If you go to support.ptc.com, Arbortext, you will see in the Quick Links at the bottom-left corner a link to the PTC Product Calendar. This will show you current, approved information regarding the release schedules. http://support.ptc.com/cs/product_calendar/PTC_Product_Calendar.htm
Major Arbortext release occur roughly every two years so I wouldn't expect Arbortext 8.0 (or 7.1?) until at least mid 2017.