The Monophthongalisation of Centring Diphthongs

In this week’s lesson on the short /ɪ/ sound, I ended the lesson on a long vowel sound with that same position [ɪː]. This is the sound that most modern speakers of GB English pronounce for words with the diphthong phoneme /ɪə/. These are the examples I used:

I’m not aware of any phonemic charts that have adopted this sound as a phoneme to replace the diphthong, but we have already seen the /eə/ diphthong replaced with long monophthong /ɛ:/ on lots of charts (including ours), so the transition from /ɪə/ to /ɪ:/ would be a logical next step. 

A similar process occured with another centring diphthong /ɔə/ which was found in words like SOURCE and BOARD, but this was monophthongalised to /ɔː/ in all British dictionaries last century. 

Changing /ɪə/ to /ɪː/ raises a couple of additional questions:

1. What to do with the remaining centring diphthong /ʊə/? 

The logical thing would be do make a long /ʊː/ phoneme which would give us a phonemic chart of short/long monophthong pairs like this:

I couldn’t think of a single minimal pair for /ʊ/ vs /ʊː/ but the /ʃʊd/ vs /əˈʃʊːd/ example is close.

2) What to do with /ɪə/ in endings such GLACIER and PERIOD? 

These are certainly not long monophthongs for any English speaker so they would need to be classified differently. My preference would be two weak vowels together /iə/ if 2 syllables are represented in the ending. Alternatively one syllable could be /jə/ giving us either /ˈpɪːriəd/ (3 syllables) or /ˈpɪːrjəd/ (2 syllables) for the word PERIOD.

This organisation of the phomemes would have the benefit of aligning the British and American charts (or any rhotic vs non-rhotic chart for that matter) as we simply have length symbols where the /r/ appears in American for all the old centring diphthongs.