The next letters on the list, if it comes to it, which it probably will, are epsilon, zeta, eta and theta. As for the desire to avoid hurt feelings, some may consider it oversensitivity. (B.1.1.7s new name is Alpha.) These old names are not abandoned. ALPHA, BETA, gamma, delta.
The next letters are presumably full of nonsensical feedback.  etaa and theta are found in a submitted research paper.
( z0 multi-sentence :snt ( z1 fill :ARG1 ( z2 letter :mod ( z3 next ) ) :ARG1-of ( z4 presume ) :ARG2 ( z5 feedback :mod ( z6 nonsense ) ) ) :snt ( z7 find :ARG1 ( z8 and :op ( z9 string-entity :name ( z10 name :op "etaa" ) ) :op ( z11 string-entity :value "theta" ) ) :location ( z12 paper :ARG1-of ( z13 submit ) :mod ( z14 research ) ) ) )
(z0 / multi-sentence
    :snt1 (z1 / fill-01
              :ARG1 (z2 / letter
                        :mod (z3 / next))
              :ARG1-of (z4 / presume-01)
              :ARG2 (z5 / feedback
                        :mod (z6 / nonsense)))
    :snt2 (z7 / find-01
              :ARG1 (z8 / and
                        :op1 (z9 / string-entity
                                 :name (z10 / name
                                            :op1 "etaa"))
                        :op2 (z11 / string-entity
                                  :value "theta"))
              :location (z12 / paper
                             :ARG1-of (z13 / submit-01)
                             :mod (z14 / research-01))))
The next letters are presumably full of nonsensical feedback . etaa and theta are found in a submitted research paper .
z2 :mod z3
z1 :ARG1-of z4
z1 :ARG1 z2
z5 :mod z6
z1 :ARG2 z5
z0 :snt1 z1
z10 :op1 0
z7 :ARG1 z8
z0 :snt2 z7
z8 :op1 z9
z9 :name z10
z11 :value 1
z8 :op2 z11
z12 :mod z14
z12 :ARG1-of z13
z7 :location z12