In his book Letter perfect: the marvelous history of our alphabet from A to Z, David Sacks says that we'll probably never decipher the Wadi el-Ḥol inscriptions (and he was probably implying the same for the Serabit el-Khadim inscriptions). Do you think we'll ever decipher them? After all, we do know that the script was an alphabet ancestral to our own, and that the language was Semitic.
It depends on what you mean by "decipher", mostly.
Many scholars agree that these inscriptions were written in some Semitic language, and that the script was ancestral to Phoenician. Gardiner's proposed interpretation of one inscription, l-bʕlt "to the lady", is also fairly well-accepted.
However, at present, the corpus is simply too small to say anything definitive. Plenty of possible translations have been offered, and there's just not enough data to accept one over another. One could argue that they've been "deciphered" many times over; we just don't know which decipherment, if any, is correct!
If more inscriptions were found, then it's likely that they could be deciphered. Linguists have gotten quite good at figuring out unknown languages based on known relatives (e.g. Akkadian, Hittite, Mycenaean). But until (and unless) that happens, it's just not possible to have much confidence in a translation.