Steps to reproduce the issue

I will be making a PR next week or earlier for this
but i would like to here any comments that may be helpful
please read on

Problem:
Forms with large number of fields can not be posted properly
because a usual limitation for max number of form fields via
-- PHP max_input_vars setting (e.g. 1000)

Expected result

Joomla 's form JS

1. counts (a rough estimation) the number of --active-- fields in the form
2. and if they are close to 1000 (we can store current real limitation in a variable e.g. into Joomla.max_input_vars),
3. then it serializes the form before it is posted
4. and then it decompresses the form at server side

Actual result

The above is not implemented and large forms can not be saved

System information (as much as possible)

Systems with PHP max_input_vars limition (e.g. a value of 1000)

Additional comments

How to do it
-- inside Joomla.submitform we attach an extra submit event handler.

NOTE:

• we cannot do it without --adding-- a submit event handler because the serialization will run before any event handlers that try to manipulate the form by listening to the submit event (thus they will not be able to see the fields (fields get disabled after serialization) , plus we will be wrongly posting field values before their processing by submit events has finished)
• and then the above mentioned submit handler cannot be attached on page load !! because this will make it run before some of the other event handlers than are listening to the submit event, (and again the same problem that was mentioned above)

so it is needed that we both

• do this work via a submit event handler
• and we also register our serialization submit handler last!!

Process

1. count active fields and continue with serialization only if close to limitation
2. serialize only the active fields and store them in a single variable (sending inactive fields is wrong)
3. disables all active fields
4. at this point in the future we can add an AJAX submit handler, this must run after serialization (i am using this too already)

on Server side we need to decompress the posted data so that they are an exact match of the original form and are identical as if form has not been serialized

• the process must restore multi-level array fields properly, even if they have some empty values

i have already written code that does the above without using eval,
but i am placing it at afterInitialize event, if anyone tries to read posted input before this then it will not be possible

• so if someone has a better idea about an earlier place where to do decompression, please answer here