Hello
The only way to import a file XAVC Long Gop which I found is to transcoder the file in XAVC Intra with Catalyst Prepare. Let us hope that SONY is going to add the codec XAVC L in VEGAS soon! Adobe Premiere Pro CC accepts the file XAVC-L (a height!)
The word on the inside is that they may allow a particular decode of a codec in the future..but you should know what the issue is underneath. The allowance of codec licensing is going to come at an increase cost to the NLE that it is embedded with. If SCS wants to hold the cost low for VegasPro - then this may be a no-brainer for marketing to bar the item. You have got to look at where VegasPro fits in the market place.
Already the license comes with Catalyst Prepare which is the broader workflow tool as well as other professional third party decoder modules that are already priced and in the pro market now.
Rumor has it ...XAVC-L codec news straight from the top at Sony (SCS) today. but can't divulge sources at this point....-We at SCS are in the process of finishing the work on VegasPro 13 XAVC L support and the plan is to have that out before the beginning of April 2015."