52mm is mount diameter or filter size. Panasonic have their own accessories like tele converter, filters etc... for FZ150 and there are third party accessories are available as well. While Canon doesn't have their own accessories for SX40 like tele converter, filters but adapter. But there are third party accessories we can use it.
Google can give plenty of links than us.
DPREVIEW
STEVEDIGICAM
FZ150 OWNERS
If it's discontinued, the successor will be priced higher. Are you ready to increase your budget? And most likely FZ150's price may fall after launching FZxxx. You can grab it then...
Generally, manufacturers launch the successor in the same interval. Like,
SX30 in Sep'10 and SX40 in Sep'11
HX100 in Feb'11 and HX200 in Feb'12
FZ100 in Jul'10 and FZ150 in Aug'11
If it continues, we can expect FZ200
soon.
What can we expect from FZ200
? FZ150 itself got everything... What would be in the upgraded version. Just guessing...
Native video support.
Better high speed recording.
It's less likely Panasonic will bring BSI CMOS as they didn't with their latest travel zoom cameras.
Increase in sensitivity
Increase in zoom which the rivals faring better
Faster shutter speed again rivals are better
GPS
Better aperture range
Better resolution screen
Increase in MP
Increase in battery life
Some extra preset modes
Macro, focus, larger Av size, flash, faster continuous shooting and all FZ150 is better even now. It's less likely FZ200 will have a better numbers in these features.