Is there a preferred way of naming the resonance hybrid in keto-enol tautomerism?
Nomenclature of Organic Chemistry, IUPAC Recommendations and Preferred names 2013 in the section P-76 DELOCALIZED RADICALS AND IONS mentions only "totally delocalized" ions like cyclopentadiene derived cyclopentadienyl radical, cyclopentadienylium cation, cyclopentadienide anion; benzo[7]annulenylium (azulenium?) and pentadienyl radical.

However, there is a draft having this chapter expanded, allowing more systematic naming of delocalized ions.


  P-76.1.2 Partial delocalization is denoted by the descriptor deloc preceded by the locants indicating the extent of delocalization. This descriptor and its locants are cited immediately before 
  the appropriate suffix and enclosed in parentheses.
  
  cyclopenta-2,4-dien(1,2,3-deloc)ide
  ...


But I am not 100% sure how exactly would that apply to your 3 structure.. let's be brave and creative:

(2Z)-but-2-en-2-(2,3,O-deloc)olate or
(2Z)-but-2-en-2-ol(2,3,O-deloc)ate or if you don't need stereochemistry
3-oxobutan-2-(2,3,O-deloc)ide or maybe even just
butanon(2,3,O-deloc)ide ? .. or
butanon(O,2,3,-deloc)ide ?

However, that draft is from 2004, but this rule did not make it into the current official nomenclature (2013), so for now we can just speculate, or contribute to the upcoming version.