οὐκ εἶπεν, ἀνεπνεύσαμεν, οὐδὲ, παρεμυθήθημεν· ἀλλὰ τί; Νῦν ζῶμεν· δεικνὺς ὅτι καὶ πειρασμὸν καὶ θάνατον οὐδὲν ἄλλο ἡγεῖται, ἢ τὸ σκάνδαλον τὸ ἐκείνων, ὄπου γε καὶ ζωὴν τὴν ἐκείνων προκοπήν. Πῶς ἄν ἄλλος τις ἢ τὴν λύπην τὴν ἐπί τῇ τῶν μαθητῶν ἀσθενείᾳ, ἢ τὴν καρὰν ἐδήλωσεν; Οὐκ εἶπε, χαίρομεν, ἀλλὰ Ζῶμεν, ζωὴν λέγων τὴν μέλουσαν.
John Chrysostom, Homily 4 on 1 Thessalonians, at 1 Thess 3:8 ("for now we live, if you stand fast in the Lord"), as trans. Broadus. =PG 62, col. 418.
"The ptc. of μέλλω is used abs. in the mng. future, to come", with a wide variety of nouns, and not infrequently by contrast with opposites like "this" or "now" (BAGD, 501, citing Mt 12:32 ("either in this age or in the age to come [(οὔτε ἐν τούτῳ τῷ αἰῶνι οὔτε ἐν τῷ μέλλοντι)]"); Eph 1:21 ("not only in this age but also in that which is to come [(οὐ μόνον ἐν τῷ αἰῶνι τούτῳ ἀλλὰ καὶ ἐν τῷ μέλλοντι)]"); 2 Clement 6:3 ("the world that is, and the world to come [(οὗτος ὁ αἰὼν καὶ ὁ μέλλων)]"); Barnabas 4:1 ("the things which now are, and . . . those which are able to save us"); 1 Tim 4:8; ("for the present life and also for the life to come [(ζωῆς τῆς νῦν καὶ τῆς μελλούσης)]"); 2 Clement 20:2 ("the life which now is, . . . that which is to come [(τῷ νῦν βίῳ, . . . τῷ μέλλοντι)]"); and so forth)).
To me it seems likely that Chrysostom introduces μέλουσαν in order to set up a play on precisely this traditional contrast; precisely, that is, in order to introduce the latter into the former in such a way as to make it clear that the life Paul experiences in the "now" ("for now we live") as a consequence of the proclamation of the exceedingly good news of Thessalonian fidelity (1 Thess 3:1-10) is in fact "the life to come".
This does not mean that Chrysostom has gone to the lengths that the Franciscan Béda Rigaux (Saint Paul: les épitres aux Thessaloniciens, Études bibliques (Paris: Librairie Lecoffre; Gembloux: Éditions J. Duculot, 1956), 480) seems to want to accuse him of having gone. For surely it is possible to experience in the "now" the life "to come" without experiencing it in some sense definitively. Indeed, surely Chrysostom, too, is pitching his tent somewhere in between, rather than at the first of the two extremes ("Il ne s'agit point de  la vie éternelle (Chrysostome . . .), mais ce n'est pas non plus  simple figure de rhétorique"), if closer to the former than Rigaux and most other modern commentators would. (And note also the range of possibilities across which, in context, the Chrysostomic commentary extends: "feel nothing of"; "were comforted", "confirmed", "anointed"; "caused us to breathe again"; "not suffered us to feel"; "further softening the expression"; etc.)