I don't have complete answer but I think that my remarks still may be useful.

Let me consider theory $\mathsf{NT}$ which extends $\mathsf{PRA}$ by one unary predicate $X$ and axiom scheme of induction in extended language and weaker theories $\mathsf{NT}_n$ in the same language but with induction scheme restricted to for $\Sigma^0_n(X)$-formulas (here $\Sigma^0_0(X)$-formulas are all the formulas from the language of $\mathsf{NT}$, where all quantifiers are bounded). The proof-theoretic ordinal $|\mathsf{NT}|$of $\mathsf{NT}$ (i.e. the limit of well-ordered order types of primitive-recursive binary relation for which $\mathsf{NT}$ proves transfinite induction for $X$) is equal to $\varepsilon_0$ (essentially it is ordinal analysis of $\mathsf{PA}$ in the terms used by W. Pohlers in his "Proof Theory. The First Step into Impredicativity", Chapter 7; Pohlers considered $\mathsf{NT}$ in the language with countable family of free unary predicates but it can't influence proof-theoretic ordinal).

Clearly,
$$|\mathsf{X}\Sigma^0_n|\ge |\mathsf{NT}_n|,$$
$$|\mathsf{RCA}|\ge |\mathsf{X}\Sigma^1_n|\ge |\mathsf{NT}|.$$

Let me consider the interpretation of $\mathsf{RCA}_0$ in $\mathsf{NT}_1$ that encodes $\mathsf{RCA}_0$-sets by $\Delta^0_1(X)$-sets. This interpretation consists of $\Pi^0_2(X)$ definition of set of codes for $\mathsf{RCA}_0$-sets and $\Delta^0_1(X)$-interpretation of $\in$. Clearly, the same syntactical translation gives an interpretation of $\mathsf{X}\Sigma^0_n$ in $\mathsf{NT}_n$ and an interpretation of $\mathsf{RCA}$ in $\mathsf{NT}$.

This interpretations gives the following bounds:
$$|\mathsf{X}\Sigma^0_n|\le |\mathsf{NT}_n|,$$
$$|\mathsf{RCA}|\le |\mathsf{NT}|.$$
Thus $|\mathsf{RCA}|=|\mathsf{X}\Sigma^1_n|=\varepsilon_0$. Also, $|\mathsf{X}\Sigma^0_n|= |\mathsf{NT}_n|$. There is natural conjecture that $|\mathsf{NT}_n|=\omega_{n+1}$, where $\omega_m$ is the tower of $\omega$-exponentiation of the height $m$. But I don't know whether it have been proved somewhere; Pohlers in Exercise 7.3.19(f) of the mentioned book asked the question about the upper bound for $|\mathsf{NT}_n|$ without definite conjecture about the answer.