Here are my ideas (so far) on Proto-Uralic syntax and inflections.
They are very tentative as of yet. First and foremost is my thesis
that Proto-Uralic was a mostly or entirely isolating language.
Secondly, it had canonical SOV word-order; however, as I have stated
before, clauses had OVS word-order (simple transfer of subject from
first position to last). It is in such clauses that Proto-Uralic's
later personal verb inflections originated.

Here are some sample Proto-Uralic sentences that I have made, using
the wordlist posted here recently:

Mi jängi elä. 'I/we carry the ice.' (Lit. '1st-person ice carry.')

Such a three-part sentence is unambiguous, given rigid SOV indicative
word-order. However, a sentence containing only two parts contains
an ambiguity:

Jängi elä.

Does it mean 'The ice carries (something)' or '(Something) carries
the ice'? It was this ambiguity that lead to the extension of a
formerly locative postposition, *ma, to be used as a general object
marker. Thus:

Mi jängi ma elä. 'I/we carry the ice.' (Lit. '1st-person ice at
Jängi ma elä. '(Something) carries the ice.' (Lit. 'Ice at carry.')
Jängi elä. 'The ice carries (something).' (Lit. 'Ice carry.')

Thus, I conclude that Proto-Uralic, unlike PIE, was never ergative;
rather, it went straight to nominative-accusative (at least with
transitive verbs).

Here is an example Proto-Uralic sentence containing a clause:

Weti ma elä mi, sä kala ma pexi. 'As I/we carry the water, she/they
cook(s) the fish.' (Lit. 'Water at carry 1st-person, 3rd-person fish
at cook.')

Later on, the grammar became more sophisticated: postpositions became
enclitic and then case suffixes, and independent pronouns became
personal verb endings. Thus:

Wetim eläpämi, kalam pexisä. 'As I/we carry the water, she/they cook
(s) the fish.'

Here the -pA ending on the verb elä 'carry' indicates a progressive
action concurrent with the action of the main verb. So a better
translation would be 'As I/we am/are carrying the water, she/they cook
(s) the fish.' I believe that the -pA ending is from an ancient
partitive suffix or postposition.

Around this time or before, grammatical number came to be deemed more
important; thus, singular and plural distinctions became formalized.
Thus, the translation of the sentence above can now be more
specific 'As I (am) carry(ing) the water, she cooks the fish.' Here
is the same sentence but with plural inflections added:

Wetim eläpämijä, kalajam pexisäjä. 'As we (are) carry(ing) the
water, they cook the fish(es).'

- Rob