Thanks for your response
If you apply for UK citizenship, then you will not be treated as non domiciled, you will then be treated as a UK resident and liable to tax on the arising basis like any other UK citizen for as long as you remain living in the UK?
At a current non UK domiciled citizen you have the right to choose how your foreign income is treated, as you have chosen to be taxed (I assume) under the remittance basis as
1) You do not declare your non UK income
2) Either have income less than £2000 or if over £2000 have had your UK personal allowances removed.
If you become a UK citizen, then you will not be treated as a non domiciled individual, as for all the time you remain living in the UK, you will need to declare all worldwide income.
That was the basis of your question was it not ?
If you move abroad then you are not resident so are not liable to UK tax anyway on foreign income but might have UK tax arising on continuing UK income (although there is scope to have this paid tax free in the UK in some instances) - but your question asked " am an EU citizen living in the UK, and am contemplating acquiring UK nationality. Is there any downside in doing it from a tax perspective? " And its on that basis I have answered your question, and then also offered further advise regarding your position of having lived in the UK for 5 years, and what that will mean for you if
1) You do NOT apply for UK citizenship and
2( Continue to be consider as liable to tax on your foreign income under the remittance basis.
Is this NOT what you are asking? As you now are asking regarding leaving the UK and severing ties - I am very confused.
I have added a link that covers all the rules here http://www.hmrc.gov.uk/international/remittance.htm
Regarding the new question regarding pensions - perhaps we could address this when we have established the first question asked.