My question is a bit broad and opinion based so I think I first have to add some of my research and analyzes in order for you to answer. I am not looking for an absolute answer, but more a "good guess" or speculations.
Most people knows about the seven ahruf, and as I generally understand it, is that the differences are pretty small and only grammatical, like for instance (2:85) "يَعْمَلُونَ" in Warsh and "تَعْمَلُونَ" in Hafs.
In the reading of Warsh, the word: "كَثِيرًا" (kathiran) is used in a verse while Hafs has another word: "كَبِيرًا" (kabiran). These almost mean the same thing and the message wouldn't really be changed, but still, they are different words.
In the tafsir of tabari, verse 49:6, it is mentioned that the word "فَتَبَيَّنُوا" (fatabayyano) was read "فَتَثَبَّتُوا" (fatathabbato) by the most reciters in Medina. Both words is argued to have the same meaning:
واختلفت القرّاء في قراءة قوله: { فَتَبَيَّنُوا } فقرأ ذلك عامة قرّاء أهل المدينة «فَتَثَبَّتُوا» بالثاء، وذُكر أنها في مصحف عبد الله منقوطة بالثاء. وقرأ ذلك بعض القرّاء فتبيَّنوا بالباء، بمعنى: أمهلوا حتى تعرفوا صحته، لا تعجلوا بقبوله، وكذلك معنى «فَتَثَبَّتُوا».
The differences found in the Sana'a manuscript, seems generally to be the same, however it seems other words are used more frequently and some words are added/deleted. For instance:
؛{يَـٰزَكَرِيَّا إِنَّا} قَد وَهَبْنَا لَكَ غُلٰماً زَكِيَّاً وَبَشَّرْنٰهُ {بِيَحْيیٰ لَمْ نَجْعَل ﻟَّ}ﻪُ مِن قَبْلُ سَمِيًّا
Sana'a manuscript (19:7)
In Hafs we have:
يَا زَكَرِيَّا إِنَّا نُبَشِّرُكَ بِغُلَامٍ اسْمُهُ يَحْيَىٰ لَمْ نَجْعَل لَّهُ مِن قَبْلُ سَمِيًّا
In the Sana'a script, the wording differs a lot while the message still is the same.
It also seems that some extra detailed words are added which doesn't exist in our texts today, lets look at one other verse in surat Maryam:
فَنٰدٮٰهَا مِن تَحْتِهَـ/ـا مَلَكٌ/ أَلَّا تَحْزَنِى
This is what we read today (in Hafs):
فَنَادَاهَا مِن تَحْتِهَا أَلَّا تَحْزَنِي
But he called her from below her, "Do not grieve;..."
So in Sana'a, the word "مَلَكٌ" (malakon) is added, i.e given the meaning "The angel called her from below her". In the tafsirs, most scholars seems to say that it was either Jesus or an Angel (Jibril) who called her.
If the manuscript was or is accepted, then the conclusion could be drawn that it indeed was an angel who called, not Jesus. But I also think that by accepting it, it would force us to rethink lots of things that we use while deriving conclusions.
More similar verses mentioned; "صَوْماً وَصُمْتاً" while we say "صَوْماً"
(19:26) ... Most commentators do explain though that sawman here means "sawtan". An example of a removed word is "وَعَلَّمْنٰهُ الْحُكْمَ" while we say: "وَآتَيْنَاهُ الْحُكْمَ صَبِيًّا". You find more examples here.
Is it likely that the sana'a manuscript was an accepted reading of the Quran?