Interesting concept , is that a huge blob of mercury rolling around in there?

This is a very old concept, AFAIK. The mercury blob is really big.

Why the arc doesn't climb into the filament ?

Perhaps because of hottest filament's parts which emit electrons -- the rest part of the filament is colder. Also, voltage is maximum at the ends of filament.

Ooh wow! this is very awesome to see! I have seen a fair pictures of these over my years browsing the internet as a lighting enthusiast, but never have I ever actually seen one lit up, thats very impressive id love to get an example in the collection, but I know they are very rare!

The parts that are hottest are result of being the arc roots. The arc can move (and the hot spots move together with it) if it would have a reason to. The "incentive" for the arc to move up is as convection pulls it up. The shorter length and lower voltage compensate for each other to some extent (limited as there is a constant voltage drop at the arc ends in all cases)

Low pressure mercury arcs usually don't even bow upward, as can be seen in germicidal fluorescent lamps, as the plasma isn't hot enough for convection currents to be made.