As i interpret the texts it is possible that an aryan can commit suicide.
There is a case where the Buddha says that one who does not take up another body is blameless if they were to use the knife.
Moreover, friend, for a long time the Teacher has been served by me in an agreeable way, not in a disagreeable way; for it is proper for a disciple to serve the Teacher in an agreeable way, not in a disagreeable way. Remember this, friend Sāriputta: the bhikkhu Channa will use the knife blamelessly.”
[ I edit out the part where Sariputta interrogates Ven. Channa ]
Then, when the Venerable Sāriputta and the Venerable Mahacunda had given the Venerable Channa this exhortation, they rose from their seats and departed. Then, soon after they had left, the Venerable Channa used the knife.
Then the Venerable Sāriputta approached the Blessed One, paid homage to him, sat down to one side, and said to him: “Venerable sir, the Venerable Channa has used the knife. What is his destination, what is his future bourn?”
“ Sāriputta, didn’t the bhikkhu Channa declare his blameless-ness right in your presence?”
“Venerable sir, there is a Vajjian village named Pubbavijjhana. There the Venerable Channa had friendly families, intimate families, hospitable families.”
“The Venerable Channa did indeed have these friendly families, Sāriputta, intimate families, hospitable families; but I do not say that to this extent one is blameworthy. Sāriputta, when one lays down this body and takes up another body, then I say one is blameworthy. This did not happen in the case of the bhikkhu Channa. The bhikkhu Channa used the knife blamelessly. Thus, Sāriputta, should you remember it. ” SN35.87: Channa
In a Sarvastivadin text (Milinda Panha) which is considered to be a part of Theravadin canon we can see a similar pattern of speech where an Arahant answers a question but the questioneer not being satisfied with the answer repeats the question. In this case the Arahant answers in the same manner as Buddha does, as "didn't you already get an answer to this question?"
An example of this is where Milinda asks Nagasena repeatedly if he was going to be born again. Ven. Nagasena initially answers saying that he will take up another body if he were to have attachment and that he wouldn't if he were otherwise. Milinda not being satisfied with the answer asks again to which Nagasena then answers akin to 'didn't i already answer your question?' and proceeds to give a simile of a man having been rewarded for his service saying that he had received nothing.
What we can infer from this Channasuttam, among other things, is that there is a case where one can lay down the body blamelessly, that is if one is an Arahant.
This is most important because of this line i the suttapitaka
Five impossibles, to wit, for an Arahant intentionally to take life... DN33: Great Recital
If we superimpose this statement with there being a possibility to lay down the body blamelessly then it is clear that suicide is not the same as killing another being.
As to whether a Sotapanna can do it, there is nothing in the Canon to suggest that that they can't as far as i know.
There is a statement in the commentary to Dhammapada saying that "Sotapannas do not kill, they don't want others to get killed" but i already showed that this would not encompass suicide.
Therefore it follows that an arahant can do, ordinary person can do and as to the stream-enterer, the reasonable assumption is that it is possible, that it can happen because it has not been proclaimed to be a disqualification.
To claim otherwise would require evidence and there is none afaik.