Okay, just to keep an update on progress with this one.....
I have tried a few 'clean upgrades' from Fabrik 2.x to 3.x and apart from a couple of very minor issues it works well.
Jupgrade is a different story though. I'll make this a sticky eventually but whilst it's fresh in my mind I'll explain, (so I can copy and paste later).
Jupgrade actually does a migration and not a physical upgrade of your site.
The end result is
jos_xxxx would be your existing Joomla 1.5 tables unless you have previously changed the prefix.
j1.7_xxxx is the new prefix of the installation jupgrade performs.
All new physical files are placed in the subdirectory /jupgrade. There is an option to specify your own subdirectory name..... but it doesn't seem to work at the moment.
Once things are working 100% I'll provide more detail, the following is only a list of the procedure and not actually how to do it.
A part of the routine makes the end 1.7 have the same prefix the 1.5 site did. This may or may not be important depending on your setup, for example jos_fabrik_tables, (which is where Fabrik stores what physical tables it's linking to), would have reference to the J1.5 prefix if you are linking to Joomla tables, (community builder for example).
So with jupgrade changing the prefix this will no longer work. Hence we change the prefix before the migration and migrate back to the jos_ prefix, (or whatever you had it set to).
01 ) Install Jupgrade on your current 1.5 site
02 ) Install akeeba Admin tools (or a utility that allows you to change table prefix)
03 ) Backup jos_fabrik_xxxx (All the main Fabrik tables)
04 ) Change database prefix to something other than jos_ (example 123_)
05 ) Change jupgrade parameters to upgrade prefix from 123_ to jos_
06 ) Run Upgrade
07 ) Delete contents of root directory (LEAVING THE JUPGRADE SUBDIRECTORY IN PLACE)
08 ) Move contents of subdirectory into root
09 ) Remove empty jupgrade folder
10 ) Remove old database tables (Anything starting with 123_xxxx)
11 ) Install Fabrik
12 ) Remove Fabrik tables starting with jos_fabrik_xxxx
13 ) Update latest github files
14 ) Restore your saved jos_fabrik_xxxx tables (that you backed up earlier point (3).
13 ) Run Fabrik upgrade. (Click Fabrik, Tools, Upgrade)
It's a little involved but because of how jupgrade does things and the physical nature of how Fabrik works it seems to be the only way at the moment.
There are still a couple of changes to be made to the Fabrik upgrade script, not bugs as such but adaptions to play nice with Jupgrade.
I'll keep you posted.......
Edit 1:-
The reason for points 07 - 10 is due to an issue when installing fabrik in the new site. For some unknown reason it tries to install into the old database. By removing the old database and files the problem is resolved.
I now believe this is an issue with jupgrade as I have installed their latest version from github and that particular problem has gone away.
This means you can run both sites in parallel during your testing phase.
www.adomain.com will be your untouched 1.5 installation and
www.adomain.com/jupgrade will be your new 1.7 version.
But.... there's always a but. Currently their latest github version only caters for 1.6 and 2.5! So you can download my version which has the correct 1.7 options.
https://github.com/felixkat/jUpgrade
.