Considering dark energy and other factors, what is the most distant object light could reach?

The most distant object that light we emit today can reach in the distant future is at the event horizon

$$eH(t) = a(t)\cdot \int_{t}^{t_{max}} \frac{c\cdot \text{d}t'}{a(t')}$$

which is now approximately 17 billion lightyears away, see the future light cone in comoving coordinates which converges to this distance:

If the light was emitted at the big bang you can use the particle horizon

$$pH(t) = \int_{0}^{t} \frac{\text{d}t'}{a(t')}$$

as the future light cone of t=0, this light has travelled some 46 billion lightyears up to now and will in the distant future converge to a comoving distance of 63 billion lightyears where the farthest galaxies it will ever reach are located today.

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The detailed calculation with the cosmological parameters from Planck 2013 can be found here from In[24] to Out[26]. For a detailed explanation of the spacetime diagram see here at page 3.