In the past, Poles used "x" instead "ks". The "x" was removed in 19th century.
Cite from the polish wikipedia: Do XIX wieku litera x była literą alfabetu polskiego na równi z pozostałymi literami, stosowana zarówno w zapożyczeniach, jak i wyrazach rodzimych (np. xięstwo), do dziś zachowała się w nazwiskach (np. Axentowicz, Jaxa, Koxowski, Mixtacki, Rexemowski, Xiężopolski) i skrótach (x. = ksiądz, książę)"
The letter <x> was polish letter on a par with the rest of the letters used in both loanwords and native words (for example: xięstwo) till 19th century. It is STILL preserved in the surnames (for example: Axentowicz, Jaxa, Koxowski, Mixtacki, Rexemowski, Xiężopolski. It is also presented in abbreviations (for exapmle: "x." means Ksiądz/english: Priest)https://pl.wikipedia.org/wiki/X
In the same manner: We don't need cyrillic letters. Poles write <s>, not <с>...
The <ѯ> is equivalent of historical <x>. Poles more and more often use the "x" in 21th century. It is present in new names, in names of companies. Poles also more often write "xero", "index", "Xymena", "expresowe" instead of "ksero" (means: a photocopy), "indeks", "Ksymena" (name: Ximen), "ekspresowe". If you want shorten "rz" to <ж>, why do you not want to short "ks" to <ѯ>?
The name "Xymena" is currently more and more written by "X" instead of "Ks". It was written by "X" in the past. Poles like short forms... Why Poles return to "X" in names now? Because the polish law hasn't denied "X" in names since 2008. I also have returned to "X" in my name (also in identity card), it is more easy for foreigners and for me.