Simplify the Table syntax

Currently, there are two syntaxes for Table:

Table:
  ( 'Table' need_input ?= 'from'
    ( 'url' url = STRING | 'file' filename = STRING )
  ) | ( 'Table' 'with' 'columns' '=' columns_tuple = Tuple
  ) | ( '(' columns += Series[','] ')' )
;

In the one syntax we get a list of Series objects (no type constraints have to be applied) and in the other - a single tuple object that holds the table columns as arbitrary objects (constraints applied only after the model is completed).

Should it be possible to keep only the one syntax?