Ok, So here comes the 1st IDIOT_Test™ (i.e. me!) of the console claiming method
TL::DR - It just works! 
Updated to add explicit separate link to instructions originally posted by Hylke above now available on a new thread here…note caution wrt gw’s bought via IoT-shop.de and/or Amazon.
Move your TTIG to V3: YES!
Had one TTIG left in lab where I had access to WiFi code so it became guinea pig. Initially registered in V2 as Genesis-S3_TestGW036_TTIG_…(additional info in description) and ran happily for a long time with 100’sk (M’s?) uplinks trafficked.
The only inconvenience was fact I like to list/describe GW’s using format Entity_DeviceID_Type_Config_Location disclaimer etc.
and it would have been nice to use part as GW ID - but rather system requires lowercase, numbers and dashes only (@descartes - you know me and my mixed case ID’s 
)
Not a problem as general settings allow more (later)
Successful claim/V3 registration:
General Settings were a bit more Jeff friendly wrt info input & use/format:
A quick power cycle for GW to get new settings and V3 registration and ~2 mins later we have traffic
With GW showing in my TTS(CE) aka TTN V3 GW list as connected
A quick check in V2 console and whilst it still shows as connected (guess that data will update and age over coming minutes and hours *update - now shows as 'unknown’) all data looks to have disappeared and now offline. Only issue is I forgot the vanity grab of handled statistics (uplink/downlink count - think this one had hit >2M uplinks)
So…RESULT! 
